Encapsulated materials

ABSTRACT

Methods and compositions for encapsulated polymeric gels swollen with nonaqueous reactive materials are provided. The methods include gel synthesis, swelling of a gel precursor with a first nonaqueous reactive material, and encapsulation of the swollen gel with a second nonaqueous reactive material. Gels precursors may be synthesized from crosslinking polymers, or alternatively, may be formed by crosslinking and polymerizing a monomer starting material. An accelerator may be utilized to facilitate swelling of the gel precursor with the first nonaqueous reactive material. Foams and composites may also be swollen with the first nonaqueous reactive material. The swollen gel is then contacted with a second nonaqueous reactive material such that an encapsulation layer is formed thereby. The encapsulated gels may be stored for subsequent use. The methods further include release of the first nonaqueous reactive material encapsulated within the gel under conditions which compromise the integrity of the encapsulation layer. The released first nonaqueous reactive material is then reacted with a nonaqueous reactive material, the reaction product being a useful product for a variety of applications such as coatings, adhesives, sealings, caulking, laminating materials, electrical coatings and the like.

This is a divisional of application Ser. No. 08/390,349 pending filed onFeb. 17, 1995.

TECHNICAL FIELD

The present invention generally relates to methods for nonaqueousencapsulating nonaqueous materials and nonaqueous compositions forencapsulated materials.

BACKGROUND OF THE INVENTION

Polymeric materials used for a variety of applications may be dividedinto "fully reacted" systems and "reactive" systems. Fully reactedsystems are those materials which are synthesized by the supplier andare delivered in finished fashion to the molder or the user. Examples offully reacted systems include polyethylene, polypropylene and nylon.Reactive systems are delivered in semi-finished or monomeric form by thesupplier to the molder or the user and undergo further reaction.Examples of reactive systems include polyurethanes (which are thereaction product of isocyanates and polyols), polyureas (which are thereaction product of isocyanates and amines or water), epoxies, reactiveacrylics, alkyds and many others.

These multi-component nonaqueous reactive systems are used extensivelyto produce polymeric coating compositions (e.g. paints), adhesives,sealants, and the like. Because the individual components react witheach other, it has been difficult to formulate nonaqueous reactivecomponent combinations which have the necessary performance properties,have the reactive capability needed to form the finished product, yethave a long shelf life under normal storage conditions. Useful reactantsare chosen on the basis of many factors and the generally recognizedproblem is that there are multiple constraints placed on the "ideal"reaction component combination. It is important to provide reactivecomponent combinations that do not sacrifice one property (e.g., longshelf life) in order to satisfy another property (e.g., reactivecapability or end-use properties).

In order to overcome these difficulties, it is common to utilizereactant systems in which the reactants are stored in separateformulations or are compartmentalized in such a manner that thereactants are combined with one another just prior to use orapplication. In one type of nonaqueous reactive chemistry, an adhesivemixture is applied to the surfaces to be joined and then either reactsspontaneously, or has the reaction rate enhanced through heat, absenceof oxygen, catalysts or other means. In another example, commonly usedequipment known in the art to formulate polyurethane coatings utilizestwo high energy component streams, i.e. a polyol and an isocyanate, thatare mixed before application. In a typical paint spray application line(see U.S. Pat. No.4,999,213), a stream of polyol and a stream ofisocyanate are mixed in an in-line mixer just before application. Underideal conditions, this mixed stream flows promptly and cleanly throughthe paint spray application equipment before any reaction occurs betweenthe polyol and the isocyanate. However, any stoppage of application ofthe paint, as often occurs, or a breakdown of the equipment, results inthe formation of soft and hard particles in the application equipment.

Other methods have been devised to compartmentalize the reactants inorder to increase the shelf life and decrease the contact time betweenthe reactants prior to actual commingling. One method is to use lessreactive pre-polymers or capped reactants such as capped isocyanategroups.

Encapsulation of reactants (e.g., isocyanate) is also used and processesare well known for producing capsules of reactive materials, exemplifiedby U.S. Pat. No. 3,409,461. It is known that highly reactive solids andreactive liquids may be compartmentalized by encapsulation through avariety of chemical and physical means including, but not limited to,interfacial polymerization in a liquid medium, in-situ polymerization,two component nozzle polymerization, centrifugal polymerization, spraydrying, fluid bed drying and rotational suspension separationencapsulation. Nevertheless, prior art encapsulation methods may requireadditional steps in preparing the reactants and impingement mixing oftwo or more reactants requiring elaborate equipment, may require hightemperatures to release the encapsulated materials, may introduceundesirable foreign materials into the product as the residue ofencapsulant and may only be suitable for certain types of reactants,such as solids. Gels have unique properties that may offer significantadvantages as compartments for reactive chemicals but, to our knowledge,encapsulation of gels containing reactive chemicals has not beensuccessfully accomplished.

Therefore, the generic problem of maintaining the integrity of severalhighly nonaqueous reactive components in a reaction mixture is stillproblematic. The specific problem of forming polymer articles such aspolyurethanes and the like under controlled conditions and at reasonablerates still has not been satisfactory resolved.

SUMMARY OF THE INVENTION

The present invention pertains, in part, to a three-dimensional, polymergel network containing a nonaqueous reactive material. The polymer gelnetwork is encased in a polymeric layer. In some cases, the layer issynthesized using a portion of the nonaqueous reactive material that isincorporated within the interstices of the polymer gel network.

Embodiments of the invention provide methods and compositions forswelling and encapsulating polymeric gel materials having nonaqueousreactive materials incorporated therein. The encapsulated gels aresuitable for storage and subsequent use. The encapsulated nonaqueousreactive material may be released and reacted with another material toprovide a variety of products for use in connection with coatings,adhesives, sealings, caulkings, laminating materials, electricalcoatings, foams, and the like. Additionally, the encapsulated materialsare suitable for use in connection with elastomeric processing byreaction injection molding for automobile fascia, bumpers, body panelsand the like. The products produced with the encapsulated gels of thepresent invention possess excellent heat resistances, chemicalresistances, electrical characteristics and abilities to withstandextreme weather conditions.

One aspect of the invention is a three dimensional, crosslinked polymergel network comprising a first nonaqueous reactive material in which thematerial is capable of entering into a spontaneous chemical reaction orcapable of catalyzing a spontaneous chemical reaction. Preferably, thefirst nonaqueous reactive material is capable of being polymerized orcapable of catalyzing a polymerization reaction. The gel network may bea responsive gel network and may for example be selected from the groupconsisting of: a gel network of poly (N,N-disubstituted acrylamide), agel network of polyacrylate esters, a gel network of polyalkylsubstituted vinyl ethers, and a gel network of polyglycol ethers or amixture thereof. The monomer(s) used to form the network may consist ofN,N-disubstituted acrylamide(s), acrylate ester(s), alkyl substitutedvinyl ether(s), glycol ether(s) or mixture thereof. The crosslinkingagent may be selected from di(ethylene glycol) bis (allyl carbonate),methylene bis (acrylamide), ethylene glycol dimethacrylate, magnesiummethacrylate and mixtures thereof.

The first nonaqueous reactive material may, for example, be selectedfrom an isocyanate, a multifunctional amine, an organometallic, an acid,an acyl halide, an acrylate and mixtures thereof. Moreover, the firstpolymeric component and the first nonaqueous reactive material togetherform a three-dimensional polymeric network in which the first polymericcomponent is capable of swelling and disgorging the first nonaqueousreactive material under predetermined conditions. It is preferred thatthe first polymeric component be nonreactive (i.e., "chemically inert")with respect to the first nonaqueous reactive material.

A further embodiment of the invention is a process of swelling a gelnetwork with a nonaqueous reactive material. The process comprisesexposing a three dimensional polymer gel network to a nonaqueousreactive material that is capable of entering into a spontaneouschemical reaction or capable of catalyzing a spontaneous chemicalreaction. Preferably, the first nonaqueous reactive material is eitherpolymerizable or is capable of catalyzing a polymerization reaction. Thestep of exposing is performed under conditions sufficient for thenonaqueous reactive material to be incorporated into the polymer gelnetwork. Preferably, prior to the step of exposing, a monomer iscombined with a crosslinking agent under conditions sufficient to form amixture and sufficient for the monomer to polymerize and form the gelnetwork.

Another embodiment is a process for swelling a gel network that includesthe steps of contacting the gel network with a gel displacing agentprior to exposure to the nonaqueous reactive material such that the gelswells and the displacing agent displaces any fluid incorporated intothe gel network. Next, the gel is collapsed with a gel collapsing agentunder conditions sufficient for the gel to disgorge the displacing agentfrom the gel network.

To facilitate the swelling process, a low molecular weight swellingaccelerator agent may be utilized. Exemplary swelling accelerator agentsinclude, but are not limited to, ketones, ethers, cyclic ethers andmixtures thereof. After the swelling process has been completed, theswelling accelerator agent is removed from the gel by vacuum strippingor the like.

A process for encapsulating a three dimensional, polymer gel network isdescribed which includes providing a three dimensional, polymer gelnetwork having incorporated in it a first nonaqueous reactive materialthat is capable of entering into a spontaneous chemical reaction orcapable of catalyzing a spontaneous chemical reaction. Preferably, thefirst nonaqueous reactive material is capable of being polymerized orcapable of catalyzing a polymerization reaction. Next, the polymer gelnetwork is exposed to one or more second nonaqueous reactive materialsunder conditions sufficient for the first material and the one or moresecond nonaqueous reactive materials to react to form a polymer layer onan outer surface of the gel network. Exemplary gel networks include agel network of a poly (N,N-disubstituted acrylamide), a gel network of apolyacrylate ester(s), a gel network of a polyalkyl substituted vinylether(s), a gel network of a polyglycol ether(s) or a mixture thereof.Preferred first nonaqueous reactive materials include isocyanates,multifunctional amines, organometallics, acyl halides, acrylates, acids,acid anhydrides. The first nonaqueous reactive material may also be acatalyst.

Another process for encapsulating a three dimensional, polymer gelnetwork comprises providing a three dimensional, polymer gel networkhaving incorporated in it a first nonaqueous reactive material. Thefirst nonaqueous reactive material is capable of entering into aspontaneous chemical reaction or capable of catalyzing a spontaneouschemical reaction. The polymer gel network is exposed to a secondnonaqueous reactive material under conditions sufficient for the secondnonaqueous reactive material to react to form a polymer layer on anouter surface of the three dimensional, polymer gel network.

Another process for encapsulating a three dimensional, polymer gelnetwork comprises providing a three dimensional, polymer gel networkhaving incorporated in it a first nonaqueous reactive material. Thefirst nonaqueous reactive material is capable of entering into aspontaneous chemical reaction or capable of catalyzing a spontaneouschemical reaction. The polymer gel network is exposed to a secondmaterial external to the gel under conditions sufficient for the secondmaterial external to the gel to react to form a polymer layer on anouter surface of the three dimensional, polymer gel network.

A further embodiment is an encapsulated polymeric gel that contains athree dimensional, polymeric gel network having incorporated in it afirst nonaqueous reactive material and a polymeric encapsulation layeron an outer surface of the gel network. The polymeric encapsulationlayer is derived from a reaction involving at least the first nonaqueousreactive material. Moreover, the encapsulation layer is capable ofproviding a barrier for the gel network and for the first nonaqueousreactive material incorporated within the network. Preferred polymericgel networks that are encapsulated include networks comprising a poly(N,N-disubstituted acrylamide), a gel network of a polyacrylateester(s), a gel network of a polyalkyl substituted vinyl ether(s), a gelnetwork of a polyglycol ether(s) or a mixture thereof. Preferred firstnonaqueous reactive materials incorporated into the gel include anisocyanate, a multifunctional amine, an organometallic, an acyl halide,and mixtures thereof, and preferred encapsulation layers arepolyurethanes, polyureas, and mixtures thereof.

Encapsulated gel networks may also include a liquid into which theencapsulated gel is immersed, the encapsulation layer providing abarrier to efflux of the first nonaqueous reactive material from the gelnetwork and a barrier to influx of the liquid into the gel network.

Polymer gel networks in which the encapsulation layer is hydrophobicsuch that the encapsulation layer acts as a barrier to water enteringthe gel network are also encompassed within the invention. In the caseof hydrophobic encapsulation layers, the encapsulation layer is alsopreferably lyophilic, so that exposure of the gel network to a secondnonaqueous reactive material is sufficient to compromise theencapsulation layer on the outer surface of the gel network.

Another embodiment of the invention is a paint system that includes athree-dimensional polymeric network having incorporated in the network afirst nonaqueous reactive material that is capable of entering into aspontaneous chemical reaction or of catalyzing a spontaneous chemicalreaction. Preferably, the first nonaqueous reactive material is capableof being polymerized or capable of catalyzing a polymerization reaction.The gel network further includes an encapsulation layer on an outersurface of the gel and a liquid into which the gel is immersed. Thefirst nonaqueous reactive material is capable of reaction with theliquid to form a reaction product which is a paint. Most preferably, thefirst nonaqueous reactive material is an isocyanate and the liquidcomprises a polyol plus additives, a dye, a pigment, a colorant and thelike. Similarly, a coating system may include the polymeric gel networkof the invention having a polymeric encapsulation layer on an outersurface of the gel and a liquid into which the encapsulated gel isimmersed. The first nonaqueous reactive material may be capable ofspontaneous reaction with the liquid to form a reaction product which isa coating material.

An adhesive material system may include the encapsulated polymericnetwork of the invention having incorporated in it a first nonaqueousreactive material that is capable of entering into a spontaneouschemical reaction or capable of catalyzing a spontaneous chemicalreaction. Preferably, the first nonaqueous reactive material is capableof being polymerized or capable of catalyzing a polymerization reaction.The first nonaqueous reactive material is capable of reaction with theliquid to form a reaction product which is an adhesive material.

A process of using an encapsulated three-dimensional polymeric gelnetwork, is also disclosed and includes the steps of providing athree-dimensional polymeric gel network having a first nonaqueousreactive material incorporated in it, the first nonaqueous reactivematerial capable of entering into a spontaneous chemical reaction orcapable of catalyzing a spontaneous chemical reaction. Preferably, thefirst nonaqueous reactive material may be polymerized or may be capableof catalyzing a polymerization reaction. The gel network furtherincludes a polymeric encapsulation layer on an outer surface of the gelnetwork. The gel network is then exposed to at least one conditionsufficient to compromise the encapsulation layer on the outer surface ofthe gel, thereby allowing the first reactive material contained in thegel to be released. A preferred process includes either exposing the gelto a second material that will either swell the gel or collapse the gelnetwork, agitating the gel network or exposing the gel to a giventemperature, pH or other trigger, any of which may compromise theencapsulation layer on the outer surface of the gel.

A further embodiment is a process of making a polymer product thatincludes providing the encapsulated three-dimensional polymeric gelnetwork of the invention that has a first nonaqueous reactive materialincorporated in the network and exposing the gel network to conditionssufficient to disgorge the first nonaqueous reactive material containedin the gel network. The disgorged first nonaqueous reactive material isallowed to contact one or more second nonaqueous reactive materialsunder conditions sufficient for the first and the one or more secondnonaqueous reactive materials to form a polymeric product from areaction between them.

A preferred process includes either exposing the gel to a secondnonaqueous reactive material that will either swell the gel or collapsethe gel network, agitating the gel network or exposing the gel to agiven temperature, pH or other trigger, all of which cause the firstnonaqueous reactive material to be disgorged from the gel network. Apolymeric product formed by this process may include a polyurethanepaint, a coating material, a foam and an adhesive material. The productmay still retain a detectable amount of the original gel network so thatanother aspect of the invention is an adhesive, a coating material, or alaminating material that includes a detectable amount of a polymeric gelnetwork incorporated in the product. This gel network may include anetwork of poly (N,N-disubstituted acrylamide), a gel network of apolyacrylate ester(s), a gel network of a polyalkyl substituted vinylether(s), a gel network of a polyglycol ether(s) or a mixture thereof.In some cases, a properly designed gel network can serve as a filler orfunctional component of the finished end-use product.

A method of coating a molded article is also encompassed within theinvention and includes the steps of providing a three-dimensionalpolymeric gel network having a first nonaqueous reactive material of theinvention incorporated in it. The gel network is exposed to conditionssufficient to disgorge the first nonaqueous reactive material and thedisgorged first nonaqueous reactive material is allowed to contact oneor more second nonaqueous reactive materials under conditions sufficientfor the first and the one or more second nonaqueous reactive materialsto form a polymeric product from a reaction between them. The moldedarticle is then contacted with the polymeric product.

A process of making a polymeric product selected from the groupconsisting of a foam, an adhesive, a coating, a paint, and a moldedarticle is also described and comprises providing a three-dimensionalpolymeric gel network having a first nonaqueous reactive materialincorporated therein, the first nonaqueous reactive material capable ofentering into a spontaneous chemical reaction or capable of catalyzing aspontaneous chemical reaction, the gel network further comprising apolymeric encapsulation layer on an outer surface of the gel network.Next, one exposes the gel network to at least one condition sufficientto compromise the encapsulation layer on the outer surface of the gelnetwork, thereby allowing the first nonaqueous reactive materialcontained therein to be disgorged and the disgorged first nonaqueousreactive material is allowed to react to form the polymeric product.

It is an object of the present invention to provide a gel which ischemically inert with respect to a nonaqueous reactive material, butwhich is capable of swelling in the nonaqueous reactive material.

It is another object of the invention to provide a method for swelling agel with a nonaqueous reactive material in which the gel is chemicallyinert with respect to the nonaqueous reactive material.

It is a further object of the invention to provide a method for swellinga gel with an isocyanate, a multifunctional amine, an acrylate, anorganometallic, acyl halide, an acid or an acid anhydride.

It is a further object of the invention to provide a method for swellinga gel with an isocyanate under accelerated conditions with the use of alow molecular weight solvent.

It is another object of the invention to provide a polymeric gel havinga nonaqueous reactive compound like an isocyanate, an acrylate,multifunctional amine, an organometallic material, an acyl halide, or anacid, an acid anhydride incorporated into the gel network.

It is another object of the invention to provide a method forencapsulating a polymeric gel having a reactive organic solvent, anacrylate, a multifunctional amine, an organometallic material, an acylhalide an acid, an acid or anhydride, incorporated into the gel network.

It is another object of the invention to provide a method forencapsulating a polymeric gel having a nonaqueous reactive material, anisocyanate, a multifunctional amine, an organometallic material, an acylhalide, an acid, an acrylate, or an acid anhydride incorporated therein,in which a portion of the nonaqueous reactive material is combined withanother reactive material to form an encapsulation layer on an outersurface of the gel.

It is another object of the invention to provide an encapsulated gelhaving a nonaqueous reactive material, an isocyanate, a multifunctionalamine, an organometallic material, an acyl halide, an acid, an acidanhydride or mixtures thereof, incorporated into the gel network, whichgels are suitable for storage and subsequent use in connection withcoatings, adhesives, foams, sealings, caulkings, laminating materials,electrical coatings and the like.

It is still another object of the invention to provide encapsulated gelscontaining a first nonaqueous reactive material, the encapsulated gelimmersed in a nonaqueous second reactive material with which the firstmaterial is capable of reacting.

It is still another object of the invention to provide encapsulated gelscontaining an isocyanate, the gels immersed in a polyol or a polyamine.

It is still another object of the invention to provide encapsulated gelscontaining a multifunctional amine, the gels immersed in an epoxyprecursor.

It is still another object of the invention to provide methods for usinga material contained within an encapsulated gel under specifiedconditions.

It is still another object of the invention to provide encapsulated gelswhich will release nonaqueous reactive components which will producepolyurethanes, epoxies, acrylates, alkyds, esters and other polymers.

It is still a further object of the invention to provide a product whichis formed by releasing a material contained within an encapsulated geland reacting the released material with at least one other materialoutside the gel.

It is still another object of the invention to provide an encapsulatedhydrophobic, lyophilic gel containing a reactive material therein,thereby providing a water-barrier for the material within the gel and aswelling medium in the presence of a compatible solvent.

It is yet another object of the present invention to provide anencapsulated gel which is thermally responsive such that the gelreversibly expands to a transparent state at an elevated temperature andcollapses to an opaque state at a lower temperature.

It is yet another object of the present invention to provide anencapsulated gel wherein the polymeric gel includes a material which isa component of a finished product.

It is yet another object of the present invention to provide a systemcontaining two or more encapsulated gels having a reactant and acatalyst contained therein.

The benefits of the use of this invention are the ability to controlnonaqueous reactive systems which have improved performance, lower cost,longer shelf life, longer pot life and improved quality.

The foregoing has outlined some of the more pertinent objects of thepresent invention. These objects should be construed to be merelyillustrative of some of the more prominent features and applications ofthe invention. Many other beneficial results can be attained by applyingthe disclosed invention in a different manner of modifying the inventionas will be described. Accordingly, other objects and a fullerunderstanding of the invention may be had by referring to the followingDetailed Description of the Preferred Embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the present invention, reference is had tothe following description taken in conjunction with the accompanyingdrawings, in which:

FIGS. 1(a)-1(c) illustrate various methods of encapsulating gels inaccordance with the present invention;

FIG. 2 is an absorbance spectrum of a solution of a phenol reddye-isocyanate (dye-tagged isocyanate) in dimethylsulfoxide (DMSO) whichillustrates the occurrence of a dye-isocyanate reaction;

FIG. 3 is an absorbance spectrum of a solution of a phenol red dye indimethylsulfoxide (DMSO);

FIG. 4 is an absorbance spectrum of dye-tagged isocyanate moleculesreleased after being encapsulated into a gel and then swollen with driedacetone according to the present invention;

FIG. 5 is an absorbance spectrum of dye-tagged isocyanate moleculesafter being encapsulated into a gel and then swollen with dried acetonein which poly(propylene glycol)bis(2-aminopropyl ether) was added to theacetone fraction containing the released dye-tagged isocyanate moleculesaccording to the present invention;

FIG. 6 is an infrared (FTIR) spectrum of dye-tagged isocyanate moleculesafter being encapsulated into a gel and then swollen with driedtetrahydrofuran (THF) in which acetone was added to the releaseddye-tagged particles in accordance with the present invention;

FIGS. 7(a) and 7(b) are infrared (FTIR) spectra of the isocyanurate formof trimeric hexamethylene diisocyanate molecules released from apolyurethane-coated poly(ethyl acrylate) gel in the presence oftetrahydrofuran (THF) according to the present invention;

FIGS. 8(a) and 8(b) respectively illustrate infrared (FTIR) spectra forthe encapsulated and non-encapsulated the isocyanurate form of trimerichexamethylene diisocyanate molecules in polyurethane-coatedpoly(diethylacrylamide) gels in a solution of tetrahydrofuran (THF);

FIGS. 9(a) and 9(b) respectively illustrate infrared (FTIR) spectra forencapsulated and non-encapsulated phenyl isocyanate molecules inpolyurethane-coated poly(dimethylacrylamide) gels in a solution oftetrahydrofuran (THF);

FIGS. 10(a) and 10(b) respectively illustrate FTIR spectra forencapsulated and non-encapsulated hexamethylene diisocyanate moleculesin polyurethane-coated poly(diethylacrylamide)gels in a solution oftetrahydrofuran (THF);

FIG. 11 illustrates the temperature dependency or thermal responsivenessof a N,N-diethylacrylamide/N,N'-methylenebis(acrylamide) (DEAAm/bis) gelin accordance with the present invention; and

FIGS. 12(a)-12(d) illustrate various electronic spectra for apoly(N,N-diethylacrylamide) gel swollen with phenol red.

Similar reference characters refer to similar parts throughout theseveral views of the drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

I. DEFINITIONS

As used herein, a "gel" is a three-dimensional, crosslinked polymernetwork containing a solvent. It is used interchangeably with the term"gel network". On the contrary, a "gel precursor" is athree-dimensional, crosslinked polymer network, preferably in dry form,which does not contain the solvent. The "solvent" is a liquid orsemi-liquid material which may be a pure material or a mixture and maycontain one or more liquids or solid solutes. In addition, a "nonaqueousreactive material" may be considered to be an organic, an inorganic oran organometallic compound or a mixture of compounds that lack asubstantial quantity of water. The reactive material is capable ofentering into a spontaneous chemical reaction or capable of catalyzing aspontaneous chemical reaction. Preferably, the first nonaqueous reactivematerial is capable of being polymerized or capable of catalyzing apolymerization reaction. The nonaqueous reactive material is thuscapable of reaction with other compounds but substantially not capableof reaction with the gel precursor or gel. Such nonaqueous reactivematerials, include, but are not limited to isocyanates, multifunctionalamines, organometallic compounds, acyl halides, acids, acid anhydrides,acrylates and the like. A "catalyst" is an organic, an inorganic, ororganometallic compound or mixture of compounds capable of modifying thereaction rate, reaction pathway or reaction completeness of one or morechemical reactions. Normally, the catalyst will either not be consumedin the chemical reaction, or will be consumed at a molar rate much lessthan that of the primary reactants.

The term "hydrophobic" as used herein in connection with a gel defines aproperty of a gel that does not swell in water or that does not collapsein water. The term "lyophilic" as used herein to defines a property of agel (i.e., a "lyogel") that swells in a nonaqueous organic solvent. Itis important to note that "lyophilicity" does not mean that the gel willswell in every organic solvent. A gel may swell in one organic solvent,but not swell in another or in mixture of solvents. It is essential toverify that the gel is "lyophilic" to the solvent being considered. Theterm "detectable amount" refers to the presence of a material in aproduct which is detectable, but which does not react with othermaterials present in the product. The term "nonaqueous" means containingno substantial quantity of water.

A "spontaneous chemical reaction" is a reaction which will proceed at ameasurable pace under the conditions of mixing of the ingredients anddoes not require addition factors such as increased temperature,pressure or light to proceed.

II. GENERAL CONSIDERATIONS

Methods of encapsulating three dimensional, polymer gel networks willnow be briefly discussed with reference to the schematic of FIGS.1(a)-1(c).

Referring now to FIG. 1(a), a three dimensional, cross-linked polymergel network 10 is provided. This polymer gel network may be synthesizedusing conventional procedures well known in the art, as discussed inmore detail below in Section III. Polymer gel network 10 is then exposedto a first nonaqueous reactive material 12. The first nonaqueousreactive material 12 has one of the following characteristics: (i) thefirst nonaqueous reactive material, most preferably an organic compound,is most preferably capable of entering into a spontaneous chemicalreaction; and/or (ii) the first nonaqueous reactive material is acatalyst, preferably an organic or an organometallic catalyst, that iscapable of catalyzing a reaction, preferably a polymerization reaction.The three dimensional polymer gel network 10 is contacted with the firstnonaqueous reactive material 12 under conditions sufficient for thefirst nonaqueous reactive material 12 to be incorporated into thepolymer gel network 10. The term "incorporated" means that the polymericgel network will be swollen by the first nonaqueous reactive material 12so that the first nonaqueous reactive material is held within the gel.

The next step in the process shown in FIG. 1(a) is the process offorming an encapsulated gel 14. The three dimensional polymer gelnetwork 10 containing the incorporated first nonaqueous reactivematerial 12 is contacted with a second nonaqueous reactive material 16that is external to the gel network 10. The second nonaqueous reactivematerial(s) 16 (see reference numeral 18 in FIG. 1(b) for additionalsecond nonaqueous reactive materials has the following properties: (i)the second nonaqueous reactive material(s), preferably an organiccompound, is capable of being polymerized; (ii) the second nonaqueousreactive material(s) may contain a catalyst, preferably an organic ororganometallic catalyst, capable of catalyzing a polymerization reactionor (iii) a mixture of materials having the properties of (i) and (ii).

Once the polymer gel network 10 containing the incorporated firstnonaqueous reactive material 12 is exposed to the second nonaqueousreactive material 16, conditions are imposed that are sufficient for aportion of the first nonaqueous reactive material 12 to efflux from thepolymer gel network 10 and contact the second nonaqueous reactivematerial 16 that is disposed external to the gel. A layer of polymericmaterial 20, hereinafter referred to as an "encapsulation layer" or"polymer layer", is formed around at least a portion of the outerperipheral surface 21 of the gel network 14, layer 20 being the reactionproduct of the first and second nonaqueous reactive materials. Thus, ifthe first nonaqueous reactive material 12 is a polymerizable organiccompound such as an isocyanate, and the second nonaqueous reactivematerial 16 includes at least a polyol and, optionally, anorganometallic catalyst, then the first and second nonaqueous reactivematerials would react to form a polyurethane layer 20 around at least aportion of the gel network. Alternatively, if the first nonaqueousreactive material were a diacid chloride and the second nonaqueousreactive material were a diamine, the first and second nonaqueousreactive materials would react to form a polyamide. In the polyurethaneexample illustrated, it will be appreciated that the polyol may beincorporated in the gel, and the isocyanate be disposed external to thegel. Normally, the nonaqueous reactive material that is readily used inthe purest form will be incorporated into the gel network. Isocyanatesare preferably incorporated into the gel network and polyols, which intypical industrial processes contain secondary substances such as dyes,pigments, colorants, additives and the like, are disposed external tothe gel network.

Without intending to be bound by any theory, it is believed that thepolymerization reaction between the first and second nonaqueous reactivematerials is self-limiting. That is, as the polymerization reactionproceeds, it deposits a layer of polymeric product 20 around the outsideof the gel 10. As polymerization reaction proceeds, the thickness oflayer 20 increases, setting up a diffusion barrier, and the efflux ofthe first nonaqueous reactive material 12 from within the gel network 10is gradually eliminated. The surficial polymerization reaction betweenthe internal contents of the gel 12 and the external contents of the gel16, 18 will eventually cease. The final result is a three dimensionalpolymer gel network 10 surrounded by a polymeric layer 20; i.e. anencapsulated gel 14.

In addition to the methods listed, there are two other general methodsof forming an encapsulated gel. The gel may be coated with two reactivematerials in succession with an "inert" material, such as a catalyst, inthe gel. Additionally, the gel may be coated with a material and asolvent. The solvent is thereafter dried, leaving the coating in place.There are many process variations in which either of these methods canbe accomplished. Referring now to FIG. 1(b), a three-dimensional polymergel network 10 is exposed to a first nonaqueous reactive material 12 (asin FIG. 1(a)),under conditions sufficient for the first nonaqueousreactive material 12 to be swollen into the polymer gel 10. Next, thepolymer gel network 10 having the first nonaqueous reactive material 12incorporated therein, is exposed to one or more second nonaqueousreactive materials 16, 18 that are external to the gel network 10. Wenote that this method may be distinguished from the method of FIG. 1(a)in that first nonaqueous reactive material 12 incorporated into thepolymer gel network 10 in FIG. 1(b) does not efflux from within the gelnetwork 10 and an encapsulation layer 20 is formed by the reaction ofthe external nonaqueous reactive materials 16, 18 with each other toform a polymeric encapsulated layer 20, i.e. an encapsulated gel 14. Itwill be appreciated that, in this embodiment, the first nonaqueousreactive material 12 inside the gel network 10 may be identical to oneof the second nonaqueous reactive materials 16, 18. It is also possiblein this case that the first nonaqueous reactive material will notspontaneously react with any of the second nonaqueous reactive materialsto form a polymeric encapsulation layer.

Alternately, the first nonaqueous reactive material 12 may participatein the polymerization reaction in the following way: a portion of thefirst nonaqueous reactive material 12 effluxes from within the gelnetwork to the surface of the gel network and reacts with secondnonaqueous reactive material 16 external to the network, therebyinitiating the formation of encapsulation layer 20. Non-aqueous reactivematerial 18 then is added to material 16 to facilitate the rate offormation of encapsulation layer 20. Nonaqueous reactive material 18 mayalso be physically separated from nonaqueous reactive material 16. Inthis case, the gel 10 having first nonaqueous reactive material 12therein is contacted with second nonaqueous reactive material 16. Next,gel 10 is then removed from nonaqueous reactive material 16 andcontacted with nonaqueous reactive material 18. Subsequent contacting ofgel 10 in nonaqueous reactive materials 16 and 18 may be desired toincrease the thickness of encapsulation layer 20.

FIG. 1(c) schematically illustrates the case where the first nonaqueousreactive material 12' is a catalyst capable of catalyzing a spontaneouschemical reaction. The most preferred catalysts are organic ororganometallic catalysts. A three dimensional polymer gel network 10 isplaced in contact with a first nonaqueous reactive catalyst 12' underconditions sufficient for the catalyst 12' to be incorporated into thepolymer gel network 10. The polymer gel network 10 incorporated with thecatalyst 12' is then contacted with a solution containing one or moresecond nonaqueous reactive materials 16, 18. In this embodiment, it ispreferable that the second nonaqueous reactive materials 16, 18 are notcatalysts but are capable of reacting with each other in the presence ofcatalyst 12'. The gel network 10 containing the catalyst 12' is exposedto conditions sufficient for at least part of the catalyst 12' to effluxfrom the polymer gel network 10 and to contact the second nonaqueousreactive materials 16, 18. A catalyzed polymerization reaction willoccur, substantially on the outer surface 21 of the polymer gel network10 to form encapsulated layer 20, i.e. an encapsulated gel 14. Asdiscussed above, it is believed that this reaction is self-limiting inthe same way as the encapsulation reaction shown in FIG. 1(a).

In sum, a polymeric gel network is contacted with a first nonaqueousreactive material such that the first nonaqueous reactive material isincorporated within the gel network. The gel network is then exposed toa second nonaqueous reactive material under predetermined conditions sothat a polymer layer or encapsulation layer is formed on an outersurface of the gel network. The polymer layer acts as a barrier andallows the gel to hold a sufficient amount of the first nonaqueousreactive material such that when the encapsulated gel is placed in asubstance with which the first nonaqueous reactive material wouldtypically react, no reaction occurs. Under predetermined conditionsdescribed below in Section VII, the integrity of the encapsulation layermay be effectively compromised in such a manner that the firstnonaqueous reactive material is released from the previouslyencapsulated gel, thereby initiating a reaction between the first andsecond nonaqueous reactive materials to form a product.

The present methodology will provide a means for making a polymericproduct using materials that cannot now currently produce the product.For example, because of its extreme reactivity at room temperature, orits extreme volatility, it may not now be possible to use a particularcompound in a polyurethane reaction. The present method of encapsulationwill enable a polymeric product to be formed using the material. It willbe appreciated that the present methods and compositions are isapplicable to any nonaqueous reactive materials that, where combined,form a desired product.

A. Responsive Gels

Preferred three dimensional polymer gel networks are responsive gelnetworks.

The term "responsive gel", in the present context, refers tothree-dimensional, polymer gel networks that are capable ofincorporating a nonaqueous reactive material into the interstitialspaces of the gel network, with a concomitant increase in gel volume.The term "responsive" is also more specifically meant to refer tothree-dimensional, permanently crosslinked gel networks known in the artto undergo volumetric changes as an external environmental condition(e.g., temperature, pH, electric field, fight intensity and wavelength,pressure, ionic strength) is changed. The polymer gel network contractsand/or expands in volume. The volume of such a gel may, under certaincircumstances, change by a factor as large as several hundred when thegel is presented with a change in external conditions.

It is well known in the art that hydrogels will exhibit these volumetricchange phenomena. See, for example, Tanaka, Physical Review Letters,Vol. 40, No. 12, pp. 820-823 (1978); Tanaka et al, Physical ReviewLetters, Vol. 38, No. 14, pp. 771-774 (1977); Tanaka et al, PhysicalReview Letters 5, Vol. 45, pg. 1636 (1980); Ilavsky, Macromolecules,Vol. 15, pg. 782 (1982); Hrouz et al, Europ. Polym. J., Vol. 17, pg. 361(1981); Ohmine et al, J. Chem. Physics, Vol. 8, pg. 6379 (1984); Tanakaet al, Science, Vol. 218, pg. 462 (1982); Ilavsky et al, Polymer Bull.Vol. 7, pg. 107 (1982); Gehrke, Responsive Gels:Volume Transitions II;ed. K. Dusek, Springer-Verlag, New York, pp. 81-144 (1993); Li et al.,Ann. Rev. Mat. Sci., 22: 243-277 (1992); and Yu et al., Enzyme Microb.Technol., 15: 354-366 (1993), all of which are incorporated herein byreference.

There is, however, relatively limited literature concerning responsivelyogels. Ansaka, et al, Macromolecules, 25, 4928 (1993) showed avolumetric change in a poly(4-vinylpyridine-styrene) gel in benzene,although an electron donor molecule needed to be dissolved in thebenzene. Shiomi, et al, Joint Symposium on Polymer Gels and Networks,Soc. Polymer Science Japan, p.40 (1993), which is incorporated herein byreference, showed that polystyrene/polydimethylsiloxane networks werealso characterized by volumetric changes as the solvent percentagecompositions were changed in mixtures of MEK and cyclohexane, benzeneand THF, and methanol and THF.

We have discovered, that, in contrast to gels undergoing volumetricchanges in hydrocarbon solvents, gels may also exhibit volumetric changephenomena in highly reactive, organic fluids such as isocyanatesolutions and polyol solutions. Therefore, particularly preferred"responsive" polymer gel networks encompassed within the presentinvention and encapsulated using the present methods are not hydrogelsat all, but are polymer gel networks that are both hydrophobic andlyophilic.

The responsive gels may also be "reversibly responsive", i.e., whenchallenged with an environmental change, the environmental changeaffects the gel by causing the entire gel, or a component thereof, toundergo a reversible volumetric change. It is preferred that the gelundergo a reversible volumetric change of at least 20 percent inresponse to a change in an environmental condition, in which the gelexpands from a less liquid-filled state or dry state at a lowertemperature to a more liquid-filled state; or collapses from a moreliquid-filled state to a less liquid-filled state. The reversible volumechange involves a shift between two equilibrium states (i.e., swollenand collapsed). The reversible volume change of the entire gel, or acomponent thereof, may be either continuous or discontinuous. A"continuous" volume change is marked by a reversible change in volume(i.e. a collapse or swelling) that occurs over a relatively large changein environmental condition. Moreover, there exists at least one stablevolume near the transition between the swollen and collapsed states.Gels may undergo a "discontinuous" volume change in which the reversibletransition from swollen to collapsed states, and back again, occurs overan extremely small change in environmental condition, such as less than0.1° C. or 0.1 pH unit. Such reversible gels are hereinafter called"phase-transition" gels. There is no stable volume between the swollenand collapsed states at the phase-transition and, in theory, theexpansion and/or collapse occurs over an infinitely small environmentalchange. A gel undergoing a continuous phase-transition may have asimilar order of magnitude total volume change as a gel undergoing adiscontinuous phase-transition.

On a molecular level, the phase transition gels are sensitive to smallchanges in a restricted repertoire of environmental "trigger" conditionsconsisting primarily of temperature. Trigger conditions are not solimited, however, and may also include pH, solvent concentration, andion concentration. On a macroscopic level, any of a variety ofenvironmental conditions may be imposed on the gel which allow thespecific trigger to induce a phase-transition. These environmentalconditions may, but not necessarily, be the same as the trigger andinclude, but are not limited to, a change in temperature, electricfield, photon energy, pH, solvent composition, ion concentration,concentration of biomolecules, pressure, and the like.

The gels may be combined with a material that acts as a molecular"transducer", converting an environmental condition into an appropriatetrigger. For example, a dye may be introduced into atemperature-triggered fast response gel. The dye is designed to absorblight of a given energy and convert the light energy into heat, thustriggering the gel to undergo a temperature induced rapidphase-transition. See also, A. Suzuki and T. Tanaka, Nature: 346: 6282(1990), incorporated herein by reference.

The volumetric changes of gels described herein result from competitionbetween intermolecular forces, usually electrostatic in nature, that actto expand the polymer network; and at least one attractive force thatacts to shrink it. Volumetric changes in gels are believed to be drivenprimarily by four fundamental forces: ionic, hydrophobic, hydrogenbonding and van der Waals bonding interactions, either alone or incombination. Each of these interactions may be independently responsiblefor a volume transition in preferred gels of the invention. Each ofthese fundamental forces is most strongly affected by a particulartrigger. Changes in solvent concentration most strongly affect the vander Waals interaction; changes in temperature most strongly affecthydrophobic interactions and hydrogen bonding; and changes in pH and ionconcentration most strongly affect ionic interactions.

Gels may be formulated in which the volume change is governed by morethan one fundamental force. In particular, gels Consisting of copolymersof positively and negatively charged groups meet this requirement. Inthese gels, polymer segments interact with each other through ionicinteractions and hydrogen bonding. The combination of these forcesresults in the existence of several pH-driven phases. See Annaka andTanaka, Nature 355: 430-432 (1992), incorporated herein by reference. Anexemplary gel of this type is a copolymer of acrylic acid andmethacryl-amido-propyl-trimethyl ammonium chloride (MAPTAC). For asummary of the properties of responsive hydrogels, see U.S. Pat. Nos.4,732,930; 4,912,032; and 5,242,491, incorporated herein by reference.

III. POLYMER GEL SYNTHESIS

Gel precursors suitable for use in accordance with the present inventioninclude various cross linked polymers, which are set forth in greaterdetail herein. Alternatively, the gel precursor may be synthesized fromthe polymerization of a monomer and a crosslinking agent. The synthesismay also include the use of an initiator and/or a promoter.

A. Gel Precursors

In principle, a gel can be made from any polymer with side groups thatcan react with a di- or multi-functional crosslinking molecule(typically in a covalent reaction, but physical interactions will alsowork). The simplest systems from which gels can be made are polymerswith hydroxyl, acid or amine side groups. Nevertheless, certain designrules are necessary for the present methods and compositions used withhighly reactive materials.

Reactive materials (i.e., isocyanates) can be characterized by the typesof chemicals with which they will react or which will catalyze theirreactions. As an example, isocyanates will react with substancescontaining an active hydrogen, a class of materials including water,alcohols, primary and secondary amines, acids, mercaptans and amidesformed from primary amines. Isocyanates can also react with some of thereaction products of isocyanates such as urethanes and ureas. The rateand degree of reaction with these materials can vary greatly frommaterial to material. Thus, a gel of N-isopropylacrylamide (NIPA) is notpreferred for use as a gel capsule for isocyanates. Nevertheless, NIPAgels would be suitable for encapsulating multifunctional amines (SeeExample 5) and catalysts (See Example 6).

It is exceedingly desirable in designing gels and gel precursors forencapsulation of nonaqueous reactive materials, especially organicmaterials, to avoid any gel/gel precursor component with which thenonaqueous reactive material can react or which will catalyze reactionor decomposition of the nonaqueous reactive material. Hydrogels that arewell known in the literature, which include polyacrylic acid, polyvinylalcohol, acrylamide, substituted acrylamides and cellulose ethers, suchas hydroxypropyl cellulose (HPC) and hydroxypropyl methyl cellulose(HPMC), contain active hydrogens and therefore are not ideallycompatible with nonaqueous reactive materials such as isocyanates.

Some gel precursors are known, however, which do not contain an activehydrogen. These materials include disubstituted acrylamides such as poly(N,N-disubstituted acrylamides) like dimethyl acrylamide, diethylacrylamide and morpholine acrylamide; acrylates, such as methylacrylate, ethyl acrylate, propyl acrylate, butyl acrylate and2-ethylhexyl acrylate; and substituted vinyl ethers, such as methylvinyl either and ethyl vinyl ether, polyacrylate ethers, polyglycolethers. These materials can exist in the presence of isocyanates and notcause reaction.

It is also important that the polymer gel network and/or gel precursornot catalyze decomposition of the nonaqueous reactive material. As anexample, vinyl pyridine contains no active hydrogen. However, as atertiary amine, it can catalyze autopolymerization of isocyanates and somust be considered unsuitable for encapsulating isocyanate. It is alsoimportant that the gel network be sufficiently lyophilic relative to thenonaqueous reactive material so that the gel is compatible with, andincorporates (e.g. by swelling) the nonaqueous reactive material.Polyethylene, polystyrene and polyvinylchloride contain no activehydrogens and do not catalyze decomposition of isocyanates. We havefound, however, that for certain isocyanates, networks containingpolyethylene, polystyrene and polyvinyl chloride are not lyophilic. Forthese reasons, these substances must be considered unsuitable gelnetworks for those isocyanates.

Finally, there must be no undesirable residue carried over within thegel network from the gel manufacturing process. As an example,crosslinked poly(dimethylacrylamide) is conveniently synthesized fromwater solution and the result is a hydrogel. When the water is removed,there is a certain quantity of "bound" water surrounding the gelnetwork, which requires additional effort and work to remove. It isessential that the bound water be completely displaced from thedimethylacrylamide gel network before it is used to incorporate a fastnonaqueous reactive isocyanate. Solvent assisted swelling followed bysolvent assisted collapsing can be used in these circumstances. SeeExample 1.

These rules apply to minor components of the gel network as well asmajor components. For example, BIS (bis methylene acrylamide) iscommonly used as a crosslinker for gel networks in concentrations from0.01 to 5% by weight of solids. Our work has shown that, as asubstituted amide present in small concentrations, BIS can be usedtogether with dimethylacrylamide for gels for encapsulating isocyanate.However, it is preferred to use crosslinkers such as DEGDA(diethyleneglycoldiacrylate) which contain no active hydrogen.

Gel precursors suitable for use in accordance with the present methodsand compositions are therefore well defined and include any componentswhich satisfy the following criteria:

1) the gel network precursor and gel network must not react with orcatalyze decomposition or reaction of the nonaqueous reactivematerial(s), i.e., the gel precursor and/or gel network contains noreactive groups;

2) the gel network must incorporate the nonaqueous reactive materialinto the network; and

3) there must be no undesirable residue (i.e. a residue that will reactwith the nonaqueous reactive material and/or will catalyze the reactionor decomposition of the nonaqueous reactive material) present from thesynthesis of the gel network itself.

Various polymers which satisfy these criteria for specific reactivechemicals are listed below, together with crosslinking agents and thelike. These should be considered as illustrative and not restrictive.

1. Exemplary gels and gel precursors

Gels may consist, in whole or in part, of polymers made bycopolymerization/crosslinking of monofunctional and polyfunctionalpolymerizable vinyl monomers. While not to be construed as limiting, themonomer may include N,N-disubstituted acrylamides such asN,N-dialkylsubstituted acrylamides, or di-N,N substituted acrylamideswhere the disubstitution form part of a ring, acrylate ethers, alkylsubstituted vinyl ethers, glycol ethers, and mixtures thereof.

Exemplary polymeric gel networks thus may contain poly(N,N-dialkylacrylamide), poly(ethyl acrylate) and mixtures thereof, aswell as polymers of N-alkylacrylamide (or analogousN-alkylmethacrylamide) derivatives such as N-ethylacrylamide,N-n-propylacrylamide, N-n-propylmethylacrylamide, N-isopropylacrylamide,N-n-isopropylmethylacrylamide, N-cyclopropylacrylamide, or acrylate (oranalogous methacrylate) copolymers like hydroxypropylacrylate-co-acrylamide, diacetone acrylamide-co-hydroxyethyl acrylate,hydroxypropyl acrylate-co-hydroxyethyl acrylate, ethylacrylamide,cyclopropylacrylamide, n-propylacrylamide, and isopropylacrylamide.

Gels may be prepared from synthetic starting materials using linearpolymers that are capable of being crosslinked. Although many of thefollowing gels contain a reactive hydrogen, the following gels may becompatible with multifunctional diamines and may be made by crosslinkinglinear polymers through physical interactions as in the poly(vinylalcohol)-poly(acrylic acid) or poly(ethylene glycol)-poly(methacrylicacid) systems, in which these hydrophobically modified polyethyleneglycols and similar polymers can associate through strong hydrophobicinteractions. Examples are poly(ethylene glycol)-poly(methacrylic acid)or poly(vinyl alcohol)-poly(acrylic acid).

Similarly, natural polymeric precursors that may be chemicallycross-linked may also be used in the invention. Exemplary polymers, someof which contain reactive hydrogens, but that may be conveniently usedwith, for instance diamines according to the invention, includeprecursors such as alkyl-substituted cellulose derivatives likecellulose ethers. Exemplary cellulose ethers include methylcellulose,hydroxyethylcellulose, methylcellulose, and hydroxypropylcellulose,hydroxypropylmethycellulose, hydroxypropylcellulose,carboxymethylcellulose and hydroxymethylcellulose. Polymers such aspolyvinylalcohol, polyethylene glycol, polypropylene glycol, andpoly(hydroxypropyldextran) are also suitable. Polypeptides likepoly(L-proline), and poly(valine-proline-glycine-X-glycine), whereX-tyrosine, phenylalanine, leucine, valine, glutamic acid, lysine,glycine, and other amino acids! may also be used.

2. Exemplary Chemical Crosslinkers

Exemplary crosslinking agents may include: ethylene glycol diacrylate(EGDA); di(ethylene glycol)bis(allyl carbonate) ("DEGBAC");methylenebis(acrylamide) ("bis"); ethylene glycol dimethacrylate("EGDMA"); magnesium methacrylate ("MgMA₂ "); and mixtures thereof.Di(ethylene glycol)bis(allyl carbonate) ("DEGBAC") and ethylene glycoldimethacrylate ("EGDMA") are commercially available from AldrichChemical Company.

The gel precursor is crosslinked and is most preferably chemicallycross-linkable. Any reagent which can react with two or more groups onthe monomer or polymer precursors can function as a crosslinker andconvert that starting material to a gel. Cross-linkers suitable forpolymeric precursors may include diglycidyl ether, divinyl sulfone,epichlorohydrin, phosphoryl chloride, trimetaphosphate,trimethylomelamine, polyacrolein, and ceric ion redox systems, althoughthe most preferred of these will not have active hydrogens. Theconcentration of crosslinkable material is generally about 0.1 to about10 mole percent based upon the polymerizable material which is the maincomponent. The crosslinking agent effects partial crosslinking of thepolymer and provides a means to control the mechanical strength, of thegel swelling degree, and intensity of volume change trigger by changingthe crosslinking density. Crosslinking of linear polymers by chemicalreagents is preferred for gels made from biological polymers such ascellulose ethers. Preferred crosslinkers for polysaccharide gels,especially cellulose ethers, are multifunctional carboxylic acids, suchas adipic acid (hexanedioic acid: HOOC(CH₂)₄ COOH), succinic acid(HOOC(CH₂)₂ COOH), malonic acid (propanedioic acid: CH₂ (COOH)₂, sebacicacid (decanedioic acid: HOOC(CH₂)COOH), glutaric acid (pentanedioicacid: HOOC(CH₂)₃ COOH), or 1,10 decanedicarboxylic acid. Dicarboxylichydroxyacids such as tartaric acid and malic acid as well asmultifunctional carboxylic acids such as 1,2,3,4-butanetetracarboxylicacid may also be suitable.

3. Exemplary Catalysts

Depending on the type of polymerization or crosslinking reaction,different types of catalysts may be required. For example, forpolymerizing vinyl monomers, polymerization initiators, such as a freeradical initiator, i.e. ammonium persulfate or sodium metabisulfite, areusually required in the present methods. For acid-base crosslinkingreactions, catalysts such as hydroxide that will catalyze reactions withpolyvinylsulfone may be required.

B. Nonaqueous Reactive Materials Incorporated into the Gel Network

While not intended to be limiting, the gel network may have incorporatedtherein nonaqueous reactive materials such as: isocyanates,multifunctional amines such as di- or triamines, organometallics, acylhalides, acrylates, polyols, acids, acid anhydrides, and mixturesthereof. More specific examples of such nonaqueous reactive materialsinclude: the isocyanurate form of trimeric hexamethylene diisocyanate,1,6-diisocyanatohexane ("HMDI"), poly(propylene glycol)bis(2-aminopropylether) ("PPGBAE") which is commercially available from Aldrich ChemicalCompany under the trade name JEFFAMINE®, adipoyl chloride ("ACI"),phenyl isocyanate ("PI"), and mixtures thereof.

C. Nonaqueous Reactive Materials External to the Gel Network

While not meant to be limiting, the nonaqueous reactive materialdisposed external to the gel, and which reacts with the incorporatedmaterial in the gel, may include polyols, polyamines, isocyanates,acids, organometallics, acid hydrides, and mixtures thereof. Forinstance, one polyol suitable for use is an oligomeric product composedof the ester formed from adipic acid and 1,4-cyclohexane dimethanol.Another nonaqueous reactive material may be poly(propyleneglycol)bis(2-aminopropyl ether) ("PPGBAE"), available from AldrichChemical Company, St. Louis, Mo.).

While each of the following components may not be preferred forincorporation into every gel, or for use external to every gel, thecomponents are provided to illustrate the type of nonaqueous reactivematerials that may be used in the present invention. Those skilled inthe art will, based on the design criteria set forth above and based onthe experimental protocols set forth herein, readily ascertain if anyparticular nonaqueous reactive material is suitable for use in theinvention.

Suitable isocyanates include any diisocyanates or polyisocyanates ormixtures thereof. Such compounds include aliphatic, cycloaliphatic,araliphatic, aromatic and heterocyclic polyisocyanates. Other exemplaryisocyanates include 4-methyl-1,3-phenylene diisocyanate, TDI, and itsdimers known under the trademark DESMODUR TT® (Bayer); 1,6-hexamethylenediisocyanate and its oligomers;1-isocyanato-3-isocyanatomethyl-3,5,5-trimethyl-cyclohexane (isophoronediisocyanate); 4,4'-diisocyanato dicyclohexylmethane and its oligomers;1,5diisocyanato-2-methylpentane and its oligomers;1,12-diisocyanatodedecane and its oligomers; and 1,4-diisocyanatobutaneand its oligomers.

Multifunctional amines are also suitable nonaqueous reactive materialsand are generally di-functional or higher, low molecular weight orrelatively high molecular weight compounds containing aliphaticallybound primary and/or secondary amino groups and having molecular weightsof from 60 to about 6000 and preferably from 60 to 3000. The preferrednonaqueous reactive amines are low molecular weight and/or relativelyhigh molecular weight primary and/or secondary polyamines, preferablydiamines. As used herein, the term "aliphatically-bound" amine groups ismeant to include amino groups attached to aliphatic groups (includingcycloaliphatic groups) or to the aliphatic residue of araliphatic groupsor in non-aromatic heterocyclic tings. In addition to the amino groups,the aliphatically-bound di- and polyamines may also contain OH-groups,tertiary amino groups, ether groups, thioether groups, urethane groups,urea groups, carboxyl groups or carboxylic acid alkylester groups.

Diamines and polyamines suitable for use may include, for example,ethylene diamine; 1,2- and 1,3-propane diamine; 1,4-butane diamine;1,6-hexane diamine; neopentane diamine; 2,2,4- and2,4,4-trimethyl-1,6-diaminohexane; 2,5-dimethyl-2,5-diaminohexane;1,10-decane diamine; 1,11-undecane diamine; 1,12-dodecane diamine;bisaminomethylhexahydro-4,7-methano-indane (TCD-diamine);1,3-cyclohexane diamine; 1,4-cyclohexane diamine,1-amino-3,3,5-trimethyl-5-amino-methyl cyclohexane (isophorone diamine);2,4- and/or 2,6-hexahydrotolyllene diamine; 2,4'- and4,4'-diaminodicyclohexyl methane; m- or p-xylylene diamine;bis-(3-amino-propyl)methylamine; bis-N,N'-(3-aminopropyll)-piperzaine;diaminoperhydroanthracenes;1-amino-2-aminomethyl-3,3,5-(3,5,5)-trimethylcyclopentane;2,2-dialkylpentane-1,5-diamines; triamines, such as1,5,11-triaminoundecane; 4-aminomethyl-1,8-diaminooctane; lysine methylester and cycloaliphatic triamines as described in GermanOffenlegungsschrift No. 26 14 244; 4,7-dioxadecane-1,10-diamine; 2,4-and 2,6-diamino-3,5-diethyl-1-methylcyclohexane and mixtures thereof;alkylated diaminodicyclohexylmethanes, for example3,3'-dimethyl-4,4'-diaminodicyclohexylmethane or3,5-diisopropyl-3',5'-diethyl-4,4'-diaminodicyclohexylmethane;perhydrogenated diaminonaphthalenes; perhydrogenated diaminoanthracenes;higher amines, such as diethylene triamine, triethylene tetramine,pentaethylene hexamine, dipropylene triamine and tripropylene tetramine;N,N'-dimethyl ethylene diamine, 2,5-dimethyl piperzine; 2-methylpiperzine; piperzine (hydrate); and 2-hydroxyethyl piperazine.

In addition to or in admixture with these relatively low molecularweight aliphatic diamines (by "relatively low molecular weight"compounds containing aliphatically-bound amino groups, is meantmolecular weights of less than 400) it is also possible to userelatively high molecular weight aliphatic di- and polyamines (i.e.,molecular weights of 400 or more) of the type obtainable, for example bythe reductive amination of polyoxyalkylene glycols with ammonia inaccordance with Belgian Pat. No. 634,741 or U.S. Pat. No. 3,654,370.Other relatively high molecular weight polyoxyalkylene polyamines may beobtained by methods of the type described in the Company Publicationentitled "Jeffamine, Polyoxypropylene Amines" by the Texaco ChemicalCo., 1978; by the hydrogenation of cyanoethylated polyoxypropyleneglycols (German Offenlegungsschrift No. 11 93 671); by the aminiation ofpolypropylene glycol sulfonic acid esters (U.S. Pat. No. 3,236,895), bythe treatment of a polyoxyalkylene glycol with epichlorohydrin and aprimary amine (French Pat. No. 1,466,708); or by the reaction ofNCO-prepolymers with enamines, aldimines or ketimines containinghydroxyl groups, followed by hydrolysis in accordance with GermanAuslegeschrift No. 25 46 536. Other suitable relatively high molecularweight aliphatic di- and polyamines are the polyamines obtainable inaccordance with German Offenlegungsschriften Nos. 29 48 419 and 30 39600 by the alkaline hydrolysis of NCO-prepolymers (with aliphaticdiisocyanates) with bases via the carbamate stage. These relatively highmolecular weight polyamines have molecular weights of from about 400 to6000, preferably from 400 to 3000 and, more preferably, from 1000 to3000.

By virtue of their structure, relatively high molecular weightpolyamines such as these are particularly suitable for the formation ofa polyurea encapsulation layer. The reaction leading to gelencapsulation are carried out at temperatures below the meltingtemperature of the particular nonaqueous reactive materials and aregenerally at temperatures below 70° C., preferably at temperatures inthe range from 0° to 50° C.

The nonaqueous reactive material may also consist of organic compoundscontaining one or, preferably more hydroxyl groups and having molecularweights of from 62 to 6000. However, it is preferred to use relativelyhigh molecular weight polyols having molecular weights in the range from400 to 6000, preferably in the range from 400 to 3000 and, morepreferably, in the range from 1000 to 3000, optionally in conjunctionwith low molecular weight polyols.

Examples of useful monoalcohols include relatively low-chain alcohols,such as isohexadecanol, and, propoxylation products of monohydricalcohols, said propoxylated products having molecular weights ofpreferably, from 4000 to 6000, (for example propoxylation products ofn-butanol). Suitable low molecular weight polyols include, for example,1,4-butane diol, 1,10-decane diol, tetra-(hydroxypropyl)-ethylenediamine or castor oil. The preferred relatively high molecular weightpolyols (i.e., molecular weights of from 400 to 6000) include forexample, polyoxyalkylene polyols, such as polyoxytetramethylene glycolsor ethoxylation and/or propoxylation products of low molecular weightdiols, polyols, diamines and polyamines. Examples include propoxylatedtrimethylol propane, propoxylated ethylene diamine or linear or branchedpolypropylene glycol ethers which may contain ethylene oxide isstatistical, block-like or terminal form.

One embodiment, for example is characterized by the use of difunctionalor higher, relatively high molecular weight polyols as a nonaqueousreactive material of the invention. When used in the synthesis ofpolyurethanes, these polyols are directly employed as reactantscontaining hydroxyl groups. Accordingly, it is also possible to use anyrelatively high molecular weight compounds containing OH-groups normallyused for the synthesis of polyurethanes as the such as polyethers,polyacetals, polythioethers and even polyesters of the type described,for example, in German Offenlegungsschrift No. 29 20 501.

IV. METHODS OF MAKING POLYMERIC GEL NETWORKS

A. General Protocol

Polymerization is initiated using a polymerization initiator, e.g., afree radical initiator such as ammonium persulfate, sodium metabisulfiteor the like, preferably with dilution with an appropriate solvent, e.g.,dimethylsulfoxide. However, neither the solvent nor the polymerizationinitiator are always important factors to obtain the polymerized productfrom the monomer mixture, and any method suitably selected fromconventionally well-known gelation methods may be applied.

Monomer starting materials are suitable, although polymeric startingmaterials are also suitable. When monomeric precursor units are used inthe methods of the invention, the polymer is formed simultaneously withpolymer crosslinking. A general protocol for forming a gel of thepresent invention using a crosslinkable, linear polymer startingmaterial includes the steps of dissolving dry linear starting materialpolymer(s) in a suitable solvent and allowing the polymer(s) and solventto mix. A crosslinking agent is then added to the polymer solution andthe solution and crosslinker are further mixed together. The resultingsolution may be poured into a solid mold (i.e., between two glassplates) and the crosslinking reaction carried out at a given temperatureregime. The gel solution may also be formed into beads or spheres usingcrosslinking in a non-solid mold where the reacting solution (polymerprecursor, crosslinker and catalysis, if needed) is dispersed in anon-solvent to form a droplet. The solution reacts within the droplet toform a bead. In this method, the non-solvent may be considered to be a"mold" for droplets. See e.g., U.S. Pat. No. 3,953,360, incorporatedherein by reference.

Gels may also be made by physically crosslinking polymerics. Forexample, polyvinyl alcohol and polyacrylic acid interact via extremelystrong, non-covalent bonding that is essentially irreversible. Gels mayalso be made by photochemical crosslinking such as exemplified by use ofultraviolet light. Nevertheless, preferred are chemically crosslinkedpolymer gel networks. "Chemically crosslinked" means that a chemicalreagent is added during synthesis which reacts with two or more polymerchains. The term "crosslinked" is meant to include gamma radiationcrosslinking as well as photochemical, electron beam, or ultravioletcross-linking.

The preferred synthesis of an encapsulated gel network from a monomergel precursor in the present invention includes mixing the monomer witha crosslinking agent, thereby forming a first solution. The monomer andcrosslinking agent may alternatively be mixed in the presence of asolvent. The first solution is then sealed and subjected to degassing ordeaeration for a predetermined period of time. See Examples 1 et seq. Asecond solution containing initiators and/or promoters may then be addedto the first solution.

Preferred solvents (for a monomer and crosslinking agent) includedimethylsulfoxide ("DMSO"), water, ethanol, toluene, THF,dimethylformamide and MEK. The monomer and crosslinking agent solutionmay be subject to degassing or deaerating by bubbling with an inert gassuch as nitrogen for a period of time long enough to ensure an absenceof oxygen and water. An initiator such as2,2'-azobis(2-methylpropionitrile) or ammonium persulfate available fromEastman Kodak Company, Rochester, N.Y. may be added to the monomer andcrosslinker solution. Alternatively, benzoyl peroxide in ethyl acrylatemay be added as an initiator. A promoter such asN,N,N',N'-tetramethylethylenediamine (available from Polysciences,) maybe included with the initiator. It should be appreciated, however, thatthe initiators and promoters listed above are exemplary only and thatother known initiators and promoters are suitable for use in accordancewith the present invention. The initiators and/or promoters may bedissolved with a suitable solvent and/or combined with a solvent such asdimethylsulfoxide ("DMSO") prior to being added to the monomer andcrosslinker solution.

V. INCORPORATION OF NONAQUEOUS REACTIVE MATERIAL INTO THE GEL NETWORK

The synthesized gel network is washed and collapsed prior toincorporation with a nonaqueous reactive material, primarily to removeundesirable solid or liquid residue from the gel network. The gelprecursor may be sectioned and the sections washed with an excess of agel displacing agent in which the gel is capable of swelling. Forexample, the gel network is sectioned into several pieces and thenwashed, and subsequently swollen, with acetone. The gel network is thencollapsed utilizing an excess of a gel collapsing agent such as toluene.Collapse of the gel will disgorge contents contained within the gelnetwork so that washing and collapsing the gel in this manner removesfluid or other impurities from within the gel network. It should beunderstood that other materials which are capable of causing the gelcomponent to swell and collapse are suitable for use in thismethodology.

Gel particles of proper size and purity are swelled with a reactivematerial. This can be done by placing the gel in an excess of reactivematerial which is to be swelled. The gel which is dry and solvent-freeis then placed in an excess of a first nonaqueous reactive material tobe incorporated therein. The gel is designed to swell in the presence ofthe first nonaqueous reactive material. Preferably, incorporation of thefirst nonaqueous reactive material is performed at room temperature. Itmay be desirable, however, to incorporate the first nonaqueous reactivematerial at an elevated temperature to accelerate the process.

To facilitate the swelling process, an accelerator may be utilized.While not meant to be limiting, ketones, ethers, and cyclic ethers aresuitable swelling agents. For example, tetrahydrofuran ("THF") or methylethyl ketone ("MEK") may be used as cosolvent and diluent for thereactive material to increase or facilitate the swelling process.Preferably, the swelling accelerator agent is a solvent having amolecular weight of less than 1000, and more preferably less than about100. The swelling accelerator agent preferably is vacuum stripped orremoved from the gel after swelling is completed. See Example 4.

VI. GEL ENCAPSULATION

The swollen gel is placed into contact with an excess of encapsulatingmaterial (i.e., a second nonaqueous reactive material) for a timesufficient to allow formation of the encapsulation layer. This isaccomplished by allowing a portion of the first nonaqueous reactivematerial incorporated within the gel network to efflux and react withthe second nonaqueous material (see FIG. 1(a)). The encapsulatingmaterial should be selected based upon the nonaqueous reactive chemicalsto be encapsulated. While not meant to be limiting, if an isocyanate isbeing encapsulated, the encapsulating material may be a polyol, apolyamine, or mixtures thereof.

The encapsulating layer may alternatively be formed by contacting a gelwith a second nonaqueous reactive material for a predetermined timeperiod and thereafter contacting the gel with another second nonaqueousreactive material (see, for instance, reference numbers 16 and 18 inFIG. 1(b)) such that a reaction occurs between the two second nonaqueousreactive materials on the outer surface of the gel network. Exposure tothe other second nonaqueous reactive material may be by dropwiseaddition into the mixture containing the gel network (see FIG. 2(b)), orby sequential contacting of the gel in the second reactive material,followed by contacting in additional second reactive material. Forpurposes of illustration, poly (N,N-dialkylacrylamide) gel particlesswollen with isocyanate may be allowed to react with polyamine orpolyol, removed therefrom and then placed in an isocyanate such that apolyurea or polyurethane encapsulated layer is produced. The process maybe repeated until a desirable encapsulation thickness is obtained.

The second nonaqueous reactive material preferably is mixed with acatalyst such as dibutyltin dilaurate (available from Aldrich ChemicalCompany). The swollen gel network may be placed in the catalyst/secondnonaqueous reactive material mixture and periodically agitated at roomtemperature until signs of hardening in the second nonaqueous reactivematerial/catalyst solution become visible. The encapsulated gel is thenseparated from the reaction materials using standard methods such ascentrifugation, filtration and the like.

In order to insure that the gel network is encapsulated with asufficient thickness of encapsulating layer, the gel preferably isplaced in a sealed container with a fresh second nonaqueous reactivematerial/catalyst mixture. The mixture preferably is maintained at roomtemperature and periodically agitated. The encapsulating layer is deemedof sufficient thickness when no further hardening of the liquidsurrounding the gel particles is observed.

The present invention may be utilized to produce a variety ofencapsulated polymer gel networks. Gels which possess hydrophobic andlyophilic properties may also be produced according to the invention. Inthis embodiment, the gel remains intact in the presence of water, i.e.,the encapsulated nonaqueous reactive material does not diffuse ortransverse the encapsulation layer and the water does not appear tosubstantially diffuse or traverse the encapsulation either. In thepresence of a compatible solvent, however, the encapsulated nonaqueousreactive material is released and reacts with the solvent.

Without intending to be bound by any theory, it is believed that theability of the encapsulated gel network to retard effusion of the fastreactive material and to retard infusion of material(s) external to thegel is not only a function of the permeability resistance of theencapsulation layer. In the case of water and the compatible solvent,the swelling of the gel network by the compatible solvent clearlyillustrates the permeability of the encapsulation layer. However, thenon-permeability of the water suggests that the hydrophobicity of thegel network and the encapsulating layer is an additional factorcontributing to the effectiveness of the encapsulation.

The present method used for nonaqueous media is not the only means forgel encapsulation. It will be understood that persons having ordinaryskill in the art may, using the techniques, design rules and protocolsdeveloped herein, adapt other methods such as in-situ polymerization,two component nozzle polymerization, centrifugal polymerization, spraydrying, fluid bed drying and rotational suspension separationencapsulation to encapsulate highly reactive nonaqueous materials ingels.

VII. RELEASE OF ENCAPSULATED NONAQUEOUS REACTIVE MATERIAL

The encapsulated gels may be stored as particles in bulk form oralternatively, in solution. Storage as solid particles, e.g. pellets,may be desirable for shipping, distribution and storage due to reducedvolume and weight. If stored in solution, the solvent may be, or maycontain, a material which is capable of reacting with the encapsulatedfirst nonaqueous reactive material when the latter is disgorged from thegel.

In general, the encapsulated gel network is exposed to conditionssufficient for the encapsulation layer to be compromised. The term"compromised" means that all, or a portion, of the encapsulation layeris broken or otherwise disrupted so that the internal contents of thegel network may come into contact with any materials external to thenetwork.

For instance, an encapsulated gel network is placed in an excess of asolvent ("swelling solvent") which is capable of compromising theencapsulation layer or coating. A swelling of the gel particles occursand is followed by the release of the encapsulated material. Theswelling solvent may be selected from a variety of solvents. Forexample, acetone, methyl ethyl ketone, tetrahydrofuran ("THF") and thelike are suitable swelling solvents so long as a sufficient swelling ofthe gel and release of the encapsulated material occurs.

The encapsulated material may also be released by shear. For instance,encapsulated gel particles may be placed into a valve or the like andsubjected to pressure such that the particles are sheared in the valve,thereby rupturing and producing small gel pieces. The encapsulatedparticles may also be released by other applications of shear. Forexample, the gel particles may be sectioned into a plurality of pieceshaving diameters of several microns. The encapsulated material may bealso the released by any of the other methods used to induce volumechange in responsive gels, including subjecting the gel network to achange in temperature, acidity, or basicity, ion or ionic strength,light, pressure and the like, (See U.S. Pat. Nos. 4,732,930, 4,912,032,et al. supra) provided the change in condition does not affect the gelnetwork in some deleterious manner.

VIII. THERMORESPONSIVE LYOGELS

The present invention also provides methods and gel compositions whichundergo temperature-induced transitions from a collapsed state to anexpanded state in neat organic solvents. The gels networks may be opaquein the collapsed state and transparent in the expanded state and thetransition from the collapsed, opaque state to expanded, transparentstate occurs because of a change from a lower to a higher temperature.See Examples 16-21.

This thermoresponsive gel network may be formed in a manner similar tothat discussed above, e.g., by deaerating a mixture of monomer andcrosslinker and adding an initiator and/or promotor.

IX. UTILITIES AND APPLICATIONS

As previously discussed, the encapsulated gels of the present inventionare suitable for storage and subsequent use in forming a variety ofuseful products.

For purposes of illustration only, encapsulated gels formed in thepresent invention may be used in injection molding processes to apply acoating or a paint layer on the molded article while the article isstill in the mold.

A gel may be inserted in a spray gun, for example, and immersed in aliquid capable of reacting with the encapsulated first nonaqueousreactive material. Application of pressure by the spray gun compromisesthe integrity of the encapsulation layer of the gel, releasing the firstnonaqueous reactive material and thereby initiating a reaction with theimmersion liquid.

One particular example is the use of isocyanate encapsulated within gelsformed in accordance with the present invention. The gels may beimmersed in a polyol (which may contain dyes, additives and the like)and subsequently placed in a spray gun or the like. Upon application ofpressure by the spray gun, the isocyanate is released and reacts withthe polyol to form a polyurethane. The polyurethane is sprayed onto themolded article in the mold or on to some other surface to the coated.

In a similar manner, the encapsulated gels may be utilized as adhesives,sealants, laminating materials, electrical coatings and the like.Moreover, encapsulated multi-functional amines released into andcontacted with multifunctional epoxy precursors are particularly usefulfor applications involving coatings and plastic encapsulants. Thepolymers produced possess excellent heat resistances electricalcharacteristics and the ability to withstand extreme weather conditions.

It should be appreciated that the methods used to release theencapsulated nonaqueous reactive material and contact anothernon-encapsulated nonaqueous reactive material may vary depending on theparticular application to be employed.

X. EXAMPLES

Reaction of isocyanates can be qualitatively measured by observing theappearance and flow behavior of the isocyanate and/or the solutioncontaining or in contact with the isocyanate. As an isocyanate reacts,its effective molecular weight increases so that it or the solutioncontaining it becomes more viscous. If the isocyanate autopolymerizes,that also will cause it to increase in viscosity or, in some cases, toharden.

Using these criteria, the viscosification or hardening of an isocyanateor isocyanate containing solution will indicate reaction of theisocyanate. Conversely, retention of the initial viscosity and flowproperties of the isocyanate can be taken to indicate lack ofpolymerization reaction. These guidelines were used in evaluating theencapsulation of isocyanates in some of the following examples.

Example 1 (Encapsulation of an isocyanate in a poly(N,N-dialkylacrylamide)-based gel with a polyol)

Encapsulation of poly(N,N-dialkylacrylamide)-based gels preswollen inisocyanates included: synthesizing, washing, and collapsing the gelfollowed by swelling in isocyanate, measurement of the effectiveswelling degree of the gel, and exposing the gel to a polyol to obtain apolyurethane layer on the outer surfaces of the gel particles. Theencapsulated isocyanate subsequently was released by compromising theintegrity of the polyurethane encapsulation layer.

1.1 Gel Synthesis

Exactly 0.73 ml (7 mmol) N,N-Dimethylacrylamide (Aldrich Corporation)and 21 μl di(ethylene glycol)bis(allyl carbonate) (DEGBAC) (Aldrich)were mixed with 9.2 ml dimethylsulfoxide (DMSO) (Aldrich) in a 20-mlvial. The mixture was then sealed with a sleeve serum stopper. Thesolution was degassed by N₂ -bubbling for 15 minutes. 100 μl of asolution of 15 mg/ml 2,2'-azobis(2-methylpropionitrile) (Eastman KodakCompany) in DMSO solution was then added to the monomer the solution.The solution was then kept at 70° C. for 20 hours resulting in atransparent gel.

1.2 Gel Washing, Collapsing and Swelling in Isocyanate

The gel prepared as set forth in 1.1 was sectioned into pieces ofapproximately millimeters in diameter and washed with excess acetone.The washing liquid was discarded and the gel was kept in acetone forabout 24 hours. The fully swollen gel then was washed with excesstoluene and was allowed to collapse in toluene for 5 days. The collapsedgel was then placed in an excess of an isocyanate containing trimerichexamethylene diisocyanate (in isocyanurate form- RHONE POULENC, HDTLC)at room temperature for about 24 hours.

1.3 Measurement of Effective Swelling Degree

Several of the gels swollen in the isocyanate were cleaned of excesssurface fluid, weighed (W_(s)), washed with excess acetone, and allowedto swell in excess acetone overnight. The swollen gel was dried at 100°C. overnight and then weighed (W_(d)). The effective swelling degree:

    S=(W.sub.s -W.sub.d)/W.sub.d ×100

was measured to be 700±100%.

1.4 Formation of Polyurethane Encapsulation Layer Formation

Gels swollen in trimeric hexamethylene diisocyanate (in isocyanurateform) were surface cleaned, weighed (W₁), and placed into an excessmixture of an oligomeric product composed of the ester formed fromadipic acid and 1,4 cyclohexane dimethanol (POLYOL) and dibutyltindilaurate catalyst (1 weight %). An oligomeric product composed of theester formed from adipic acid and 1,4 cyclohexane dimethanol isavailable from KINJ Industry (K-FLEX188). Dibutyltin dilaurate isavailable from Aldrich Corporation. The mixture was kept in a sealedvial at room temperature and periodically checked until the polyolsolution began to harden. The encapsulated gel was taken out of thepolyol/catalyst mixture, surface cleaned, weighed (W₂), and placed intoa fresh mixture of an oligomeric product composed of the ester formedfrom adipic acid and 1,4 cyclohexane dimethanol and dibutyltin dilaurate(1 w %). The weight gain:

    WG=(W.sub.2 -W.sub.1)/W.sub.1 ×100

was measured to be 10-15%. The encapsulated gels were allowed to remainin the polyol/catalyst mixture in a sealed vial at room temperature andperiodically shaken for 7 days. No hardening of the liquid surroundingthe gels was observed.

Example 2

A poly (N,N-dialkylacrylamide)-based gel swollen with an isocyanatecontaining trimeric hexamethylene diisocyanate (in isocyanurate form)was prepared as set forth above in steps 1.1 to 1.3. The swollen gelswere surface cleaned, weighed (W₁), and briefly (for 2-3 seconds) placedinto an excess of poly(propylene glycol)bis(2-aminopropyl ether)("PPGBAE") having an average molecular weight of 230. PPGBAE isavailable from Aldrich Corporation. The gels were then removed andcontacted with an isocyanate (HDTLV RHONE POULENC) for about 2-3seconds. Formation of a polyurea layer around each particle wasimmediate. The gels were again contacted with PPGBAE and isocyanate andthen the encapsulated gels were placed into a sealed vial at roomtemperature overnight in order to complete formation of the polyurealayer. The encapsulated gels were weighed (W₂) and placed into themixture of an oligomeric product composed of the ester formed fromadipic acid and 1,4 cyclohexane dimethanol and dibutyltin dilaurate (1 w%). The weight gain:

    WG=(W.sub.2 -W).sub.1 /W.sub.1 ×100

was measured to be 50-70%. The encapsulated gels were placed in thepolyol/catalyst mixture in a sealed vial at room temperature andperiodically checked for 7 days. No hardening of the liquid surroundingthe gel particles was observed.

Example 3

Non-encapsulated gels were swollen in isocyanate containing trimerichexamethylene diisocyanate (in isocyanurate form) as described above inExample 1. These gels were then placed into a mixture of an oligomericproduct composed of the ester formed from adipic acid and 1,4cyclohexane dimethanol and dibutyltin dilaurate (1 w %) and kept in asealed vial at room temperature and periodically shaken. Hardening ofthe polyol/catalyst mixture surrounding the gels was observed withinabout 3-4 hours.

An isocyanate containing trimeric hexamethylene diisocyanate (inisocyanurate form) was added dropwise into the mixture of an oligomericproduct composed of the ester formed from adipic acid and 1,4cyclohexane dimethanol and dibutyltin dilaurate (1 w %) and the solutionwas kept in a sealed vial at room temperature and periodically checked.Hardening of the entire solution was completed within 1-2 hours.

3.1 Tagging Procedure for Monitoring Isocyanate Release by UV/VisibleSpectroscopy.

A 1 ml solution of 0.42 g/ml Phenol Red (Aldrich) in DMSO was mixed with138 g of an isocyanate containing trimeric hexamethylene diisocyanate inisocyanurate form to give 3 mg/g solution. Phenol Red is hereinafterreferred to as "dye". Control tests showed that DMSO is an excellentsolvent for the dye.

The dye-in-isocyanate solution was shaken and kept at 70° C. for 3 days.The unreacted dye was allowed to settle, and the UV/visible spectra ofcolored isocyanates were recorded. (Shimadzu UV-16012, Quartz Cuvets,1.0 cm path length). As shown in Table 1 and FIG. 2, the absorbancespectra of the tagged isocyanate revealed λ_(max) 378 nm, A₃₇₈ 0.78.(see Table 1-λ_(max) =376 at Amax=0.78). In contrast, the absorbancespectra of the dye in DMSO without isocyanate added revealed λ_(max) 406nm, A₄₀₆ 0.79. (see Table 2 and FIG. 3). The observed 30 nm shiftindicates significant perturbance of the electronic environment of thedye and suggests that the dye-isocyanate reaction took place.

                  TABLE 1                                                         ______________________________________                                        Absorbance spectra of the tagged isocyanate (dilution by DMSO).               No.     Dilution, times λ.sub.max, nm                                                                   A.sub.max                                    ______________________________________                                        1       --              398      >3                                           2       2               401      >3                                           3       5               378      >2                                           4       15              376      0.78                                         ______________________________________                                    

                  TABLE 2                                                         ______________________________________                                        Absorbance spectra of the Dye in DMSO.                                        No.    Dye concentration mg/g                                                                          λ.sub.max, nm                                                                   A.sub.max                                   ______________________________________                                        1      3                 449      >3                                          2      1                 454      >3                                          3      0.5               416      >3                                          4      0.2               410      >2                                          5       0.03             406      0.79                                        ______________________________________                                    

3.2 Solvent-Triggered Release of the Tagged Isocyanate as Demonstratedby UV/Visible Spectroscopy

Poly(dimethylacrylamide) gel (1.2 mol % crosslinking bymethylenebis(acrylamide)) was allowed to swell in a tagged isocyanatesolution containing trimeric hexamethylene diisocyanate (in isocyanurateform) for 2 days. The gel swollen in the tagged isocyanate was placed inan excess mixture of an oligomeric product composed of the ester formedfrom adipic acid and 1,4 cyclohexane dimethanol and dibutyltin dilaurate(catalyst, 1 w %). The mixture was kept in a sealed vial at roomtemperature and periodically checked until the polyol solution began toharden. The encapsulated gels were removed from the polyol/catalystmixture, surface cleaned, and placed into a fresh mixture of anoligomeric product composed of the ester formed from adipic acid and 1,4cyclohexane dimethanol and dibutyltin dilaurate (1 w %). Theencapsulated gels were left in the polyol/catalyst mixture in a sealedvial at room temperature and periodically checked for 2 days. Nohardening of the liquid surrounding the gels or release of yellow colorinto the polyol surrounding the gels was observed. This suggests thatthe encapsulation layer provided an effective barrier for the gels inthe polyol solution.

Several encapsulated gels were then taken out of the mixture and placedin excess dried acetone. Swelling of the gels, followed by the releaseof a yellow/orange colored compound within 2-3 hours was observed. Asillustrated in FIG. 4, the released compound possessed maximumabsorbance at 374 nm in the electronic spectrum, thereby indicating thatthe released compound was essentially the dye-tagged isocyanate (comparewith the spectrum of the tagged isocyanate with λ_(max), nm at 376 nm).Reactivity of the released species was confirmed by addition ofpoly(propylene glycol)bis(2-aminopropyl ether) (available from AldrichCorporation as JEFFAMINE® D-230) into the acetone fraction whichcontained the released dye-colored isocyanate. Upon addition ofJEFFAMINE® D-230, the solution turned violet and relevant peaks in theelectronic spectrum were observed: λ_(max), nm at 576 and 416 as shownin FIG. 5.

3.3 Solvent Triggered Release of the Gel-Encapsulated Isocyanate asDemonstrated by FTIR.

Poly (dimethylacrylamide) gel (1.2 mol % crosslinking bymethylenebis(acrylamide)) was allowed to absorb tagged isocyanatecontaining trimeric hexamethylene diisocyanate (in isocyanurate form)for 15 days. Several of the gel particles swollen in the taggedisocyanate were placed into an excess mixture of an oligomeric productcomposed of the ester formed from adipic acid and 1,4 cyclohexanedimethanol and dibutyltin dilaurate (catalyst, 1 w %). The mixture waskept in a sealed vial at room temperature and periodically checked untilthe polyol solution began to harden.

Approximately 1.2 g of encapsulated gels were removed from thepolyol/catalyst mixture, surface cleaned, and placed into the mixture ofan oligomeric product composed of the ester formed from adipic acid and1,4 cyclohexane dimethanol and dibutyltin dilaurate (1 wt %). Theencapsulated gels remained in the polyol/catalyst mixture in a sealedvial at room temperature and were periodically checked for a day.Hardening of the liquid surrounding the gel particles was not observed,indicating that the encapsulation layer provided an effective barrierfor the gel in the polyol solution.

Several of the encapsulated gels were then taken out of the mixture andplaced into 4 ml of anhydrous tetrahydrofuran (THF). Swelling of gelswas observed within 3 days. The FTIR spectrum of the released compoundin THF revealed the presence of intact isocyanate component as shown bypeaks at approximately 2270 cm⁻¹ in FIG. 6.

3.4 Polyurethane Formation Through Shear Triggered Release

Poly(dimethylacrylamide) gel (1.2 mol % crosslinking bymethylenebis(acrylamide)) was allowed to absorb colored isocyanatecontaining trimeric hexamethylene diisocyanate (in isocyanurate form) inmethyl ethyl ketone (1:1 v/v) for 2 days. The methyl ethyl ketone thenwas removed from the gels by vacuum stripping such that coloredisocyanate remained in the gels. The gels swollen in the coloredisocyanate were placed into an excess mixture of an oligomeric productcomposed of the ester formed from adipic acid and 1,4 cyclohexanedimethanol and dibutyltin dilaurate (catalyst, 1 wt %). The mixture waskept in a sealed vial at room temperature and periodically agitateduntil the polyol solution began to harden. The encapsulated gels wereremoved from the polyol/catalyst mixture, surface cleaned, weighed, andplaced into the mixture of an oligomeric product composed of the esterformed from adipic acid and 1,4 cyclohexane dimethanol and dibutyltindilaurate (1 wt %). The encapsulated gels were allowed to stay in thepolyol/catalyst mixture in a sealed vial at room temperature andperiodically agitated for 24 hours. Hardening of the liquid surroundingthe gel particles was not observed, indicating that the encapsulationlayer had formed.

Several of the encapsulated gels were then taken out of the mixture andplaced into a pipe with a needle valve on the downstream side. Uponapplication of air pressure (≦45 PSIG), gel particles were transportedacross the shear zone of the valve, to produce small gel pieces at theoutlet. The broken gel particles quickly hardened at 60° C. whichconfirmed the reactivity of the isocyanate exposed to the gel surface.

Example 4

In this example, an isocyanate is swollen in a poly(ethylacrylate)-based gel and encapsulated with polyol, followed by triggeredrelease of fully nonaqueous reactive isocyanate.

4.1 Gel Synthesis

A mixture of 5.0 ml (46.1 mmol) ethyl acrylate (EtAc, monomer), and 50μl of 0.0226 ml/ml solution of ethylene glycol dimethacrylate (EGDMA,5.99 μmol, crosslinker) in dimethylsulfoxide (DMSO) was deaerated by N₂bubbling for about 0.5 hours. Approximately 100 μl of freshly preparedsolution of 100 mg/ml benzoyl peroxide in ethyl acrylate was added, andthe resulting solution was stirred and maintained at 70° C.Polymerization was observed after approximately 2 hours, however, thesolution with the forming polymer was allowed to stay at 70° C.overnight. The formation of a crosslinked polymeric gel network wascompleted within a day at 70° C.

4.2 Isocyanate Loading

A cube-shaped piece of the gel network produced above in Section 4.1 (98g dry weight) was placed into an excess mixture of 1 g of trimerichexamethylene diisocyanate (in the isocyanurate form) per 1 ml of THF.The gel was allowed to swell in the mixture for 5 days at roomtemperature. The weight of the swollen gel was measured to be 958 mg,or, a total uptake of 877%. The swollen gel was dried under high vacuumfor 3 hours. The weight of the dried gel was measured to be 315 mg suchthat the isocyanate uptake was about 220%.

4.3 Gel Encapsulation

The gels swollen with isocyanate as in Section 4.2 were placed into avial containing an excess of an oligomeric product composed of the esterformed from adipic acid and 1,4 cyclohexane dimethanol and dibutyltindilaurate (1 w % in polyol) for 4 hours at room temperature. We observedsigns of hardening of the liquid surrounding the gels. Afterencapsulation, we observed a transparent viscous polymeric film aroundeach gel. Encapsulated gels were removed from the polyol/catalystmixture and placed into a separate vial containing a freshpolyol/catalyst mixture. No signs of hardening of the polyol/catalystmixture contacting the encapsulated gels were observed over a period ofone month and longer, thereby evidencing encapsulation efficiency.

4.4 Test of Active Isocyanate Released from Encapsulated Gel

Encapsulated gels (see Section 4.3) were weighed and placed into dry THFin such a way that the gels constituted a suspension of 40 mg of gel per1 ml of THF. The gels in the THF were constantly agitated for about 3hours. The gels exhibited significant swelling.

THF solutions surrounding the gels were analyzed by means of FTIR on aPerkin-Elmer Model 1620 spectrometer applying AgBr crystals. As shown inFIG. 7, we observed a peak at 2270 cm⁻¹ (--N═C═O vibrations), which isvery strong evidence of unreacted isocyanate present in the solution.

ENCAPSULATION OF MULTIFUNCTIONAL AMINES INTO GELS FOLLOWED BY TRIGGEREDRELEASE OF AMINES

Reactions between di- or triamines and multifunctional (typically, di-or trifunctional) epoxy compounds represent the type of nonaqueousreactive chemistry widely used in the coating industry, for plasticencapsulants, and the like.

Example 5

5.1 Gel Swelling and Encapsulation

In this example, poly(propylene glycol)bis(2-aminopropyl ether) havingthe following formula:

    CH.sub.3 CH(NH.sub.2)CH.sub.2  OCH.sub.2 CH(CH.sub.3)!.sub.n NH.sub.2,(1)

was utilized to illustrate encapsulation of a diamine.N,N'Dimethylacrylamide (DMAAm),-based gels and N-isopropylacrylamide(NIPA)-based gels were prepared using conventional methods with variouscrosslinkers such as: methylenebis(acrylamide) (bis), magnesiummethacrylate (MgMA₂), and di(ethylene glycol)bis(allyl carbonate)(DEGBAC). DMAAm-based gels were synthesized in DMSO, washed with acetoneand collapsed with toluene. NIPA-based gels were synthesized in waterand then dried. Examples of swelling of different gels for 2 days incompound (1) are shown in Table 3. Diamine uptake was estimated usingthe formula:

    Uptake, %=(W.sub.s -W.sub.d)/W.sub.d.sup.× 100,

where W_(s), mg is the weight of the swollen gel, and W_(d), mg is theweight of dry polymer obtained by extracting the diamine from the gel byexcess acetone followed by drying the gel at 70° C. for about 12 hours.

                  TABLE 3                                                         ______________________________________                                        Diamine Uptake by Gels                                                                       Weight dry,                                                                             Weight swollen,                                                                           Uptake                                   Sample         mg        mg          %                                        ______________________________________                                        DMAAm gel crosslinked by                                                                     4.3       140         3160                                     DEGBAC         5.6       166         2860                                                    5.1       170         3230                                     DMAAm gel crosslinked by                                                                     4.4       198         4400                                     MgMA.sub.2                                                                    DMAAm gel crosslinked by                                                                     5.0       107         2040                                     bis            6.6       158         2290                                     NIPA gel crosslinked by bis                                                                  12        143         1090                                     ______________________________________                                    

Gel particles swollen in the diamine were placed into trimerichexamethylene diisocyanate for 10-15 seconds and then quickly removedand placed into a fresh aliquot of diamine where a whitish viscouspolyurea layer formed immediately around each of the gel particles.Depending on the thickness of the polyurea layer desired, the process ofplacing particles into isocyanate and diamine may be repeated to thickenthe polyurea layer around the particles. The encapsulated gels wereremoved from the liquid and kept in air overnight where theencapsulating polyurea layer hardened. Examples of encapsulation ofvarious gel systems resulting in a weight gain by gels are shown inTable 4.

                  TABLE 4                                                         ______________________________________                                        Weight Gain of Gels Resulting from Encapsulation                                       Weight, swollen                                                                           Weight, swollen and                                                                         Weight gain,                               Sample   in diamine, mg                                                                            then encapsulated, mg                                                                       %                                          ______________________________________                                        DMAAm gel                                                                              125         230           83                                         crosslinked by                                                                DEGBAC                                                                        DMAAm gel                                                                              105         167           59                                         crosslinked by                                                                bis                                                                           NIPA gel  66         117           77                                         crosslinked by                                                                bis                                                                           ______________________________________                                    

5.2 Encapsulation Test

The encapsulated gels formed in Section 5.1 were then tested todetermine whether the encapsulation procedure effectively preventedrelease of dime into nonaqueous reactive mixtures. Encapsulated gelswere introduced into an epoxy solution,N,N-diglycidyl-4-glycidyloxyaniline, at 20° C.N,N-diglycidyl-4-glycidyloxyaniline is available commercially fromAldrich Corporation. We observed hardening of the resulting mixturewithin 1-2 hours. In the control experiments without any gel, thediamine and epoxy compound were quickly mixed and complete hardening ofthe mixture was observed within 20-30 minutes.

5.3 Test of Solvent-Triggered Release of Diamine from Encapsulated Gels

The following test was conducted in order to ensure proper release ofthe diamine encapsulated in the gels prepared according to Section 5.1,and to establish the capability of the diamine to polymerize uponswelling and be released from the gel upon contact with acetone. Acetoneis a swelling agent for DMAAm. Encapsulated gels were kept in anhydrousacetone for 2 days at 20° C. The gel systems utilized for this test areshown in Table 5.

                  TABLE 5                                                         ______________________________________                                        Gel Systems Used in Testing of Solvent-Triggered Release                      of the Diamime                                                                                       Weight of  Volume of                                   ID                     encapsulated                                                                             dry acetone                                 No.  Sample            gel, mg    added, ml                                   ______________________________________                                        1    DMAAm gel crosslinked by                                                                        126        3                                                DEGBAC                                                                   2    DMAAm gel crosslinked by bis                                                                     98        3                                           3    NIPA gel crosslinked by bis                                                                     164        3                                           ______________________________________                                    

Following disruption of the encapsulation layer by swelling in acetonefor 2 days, 1 ml of the solution surrounding the gels was withdrawn andplaced into 2 ml of an epoxy compound (as in 5.2) at 20° C. Completehardening of the mixture was observed overnight. In the controlexperiments without any gel, 1 ml of dry acetone was placed into 2 ml ofepoxy compound at 20° C. No complete hardening of the mixture wasobserved overnight.

ENCAPSULATION OF CATALYSTS INTO GELS FOLLOWED BY TRIGGERED RELEASE OFCATALYSTS Example 6

In this example, a catalyst was encapsulated in a gel and then, thecatalyst was released into a reactive medium in order to induce apolymerization reaction.

6.1 Gel Swelling and Encapsulation

Dibutyltin dilaurate having the following formula:

     CH.sub.3 (CH.sub.2).sub.10 CO.sub.2 !.sub.2 Sn (CH.sub.2).sub.3 CH.sub.3 !.sub.2                                                   (2)

is widely used as a catalyst for elastomeric processing by reactioninjection molding for automobile fascia, bumpers, body panels and thelike. Dimethylacrylamide (DMAAm)-based and N-isopropylacrylamide(NIPA)-based gels were prepared using various crosslinkers, includingmethylenebis(acrylamide) (bis), magnesium methacrylate (MgMA₂), anddi(ethylene glycol)bis(allyl carbonate) (DEGBAC). DMAAm-based gels weresynthesized in DMSO, washed with acetone and collapsed by toluene. NIPAgels were synthesized in water and then dried. A cellular materialconsisting of polyurethane foam, was also tested to determine catalystuptake. Examples of swelling for 3 days of different gels and foam areillustrated in Table 6. Catalyst uptake was estimated using the formula

    Uptake, %=(W.sub.s -W.sub.d)/W.sub.d.sup.× 100,

where W_(s) (mg), is the weight of the swollen gel, and W_(d) (mg), isthe weight of dry polymer obtained by extracting the catalyst from thegel using excess acetone followed by drying the gel at 70° C. for about12 hours.

                  TABLE 6                                                         ______________________________________                                        Catalyst Uptake by Gels and a Foam                                                                    Weight swollen,                                       Sample       Weight dry, mg                                                                           mg          Uptake, %                                 ______________________________________                                        DMAAm gel crosslinked                                                                      7.9        32          310                                       by DEGBAC    7.8        28          250                                                    46         180         290                                       DMAAm gel crosslinked                                                                      13         39          200                                       by MgMA.sub.2                                                                              6.2        22          250                                       DMAAm gel crosslinked                                                                      50         150         190                                       by bis       42         130         210                                       NIPA gel crosslinked                                                                       14         35          150                                       by bis       7.5        23          210                                       Polyurethane foam                                                                          17         110         550                                                    21         150         610                                       ______________________________________                                    

Either the gel or the foam swollen in the catalyst were then placed intotrimeric hexamethylene diisocyanate for 10-15 seconds and then quicklytaken out and placed into poly(propylene glycol)bis(2-aminopropyl ether)having the formula:

    CH.sub.3 CH(NH.sub.2)CH.sub.2  OCH.sub.2 CH(CH.sub.3)!.sub.n NH.sub.2,(3)

where a whitish viscous polyurea layer formed immediately around the gelor foam particles. Depending on the thickness of the polyurea layerdesired, the process of placing particles into isocyanate and diaminemay be repeated to thicken the polyurea layer. The encapsulatedmaterials were removed from the liquid and kept in air overnight wherethe encapsulating polyurea layer hardened. Weight gain by the gels areshown in Table 7.

                  TABLE 7                                                         ______________________________________                                        Weight Gain of Gels Resulting From Encapsulation                                         Weight, swollen                                                                           Weight, swollen and                                                                         Weight                                   Sample     in catalyst, mg                                                                           then encapsulated, mg                                                                       gain, %                                  ______________________________________                                        DMAAm gel cross-                                                                         260         450           73                                       linked by DEGBAC                                                              DMAAm gel cross-                                                                         140         230           64                                       linked by bis                                                                 NIPA gel cross-                                                                          110         160           45                                       linked by bis                                                                 ______________________________________                                    

6.2 Encapsulation Test

In order to determine whether the encapsulation procedure described inSection 6.1 effectively prevented the release of catalyst into reactivemixtures, the following test was conducted. Encapsulated gels containingcatalyst were added into an oligomeric product composed of the esterformed from adipic acid and 1,4 cyclohexane dimethanol. Then, anisocyanate containing trimeric hexamethylene diisocyanate (inisocyanurate form) was quickly added. The resulting mixtures originallyat about 20° C. were immediately placed into 60° C. oven where hardeningof the liquid surrounding the encapsulated gels was monitored. Theresults of the encapsulation test are shown in Table 8. "+" representscomplete hardening which manifests polymerization of isocyanate/polyolmixture within 5.0 min at 60° C., and "-" represents the absence ofobserved changes in the polyol/isocyanate mixture under identicalconditions.

                  TABLE 8                                                         ______________________________________                                        Results of Encapsulation Test                                                             Weight of                                                                     encapsulated                                                                            Weight of                                                                              Weight of                                      Sample      gel, mg   polyol, g                                                                              isocyanate, g                                                                         Result                                 ______________________________________                                        DMAAm gel cross-                                                                          180       2.8      1.9     -                                      linked by DEGBAC                                                              DMAAm gel cross-                                                                          230       3.1      2.5     -                                      linked by bis                                                                 NIPA gel crosslinked                                                                      160       3.6      3.9     -                                      by bis                                                                        Control 1   --        4.4      2.8     -                                      Control 2   --        3.8      2.6     +                                                            40 mg                                                                         catalyst                                                                      added                                                   ______________________________________                                    

6.3 Test of Solvent-Triggered Release of Catalyst from Encapsulated Gel

This experiment demonstrated that the release of the catalystencapsulated in the gels prepared according to Section 6.1 would becapable of inducing polymerization upon solvent (acetone) triggeredrelease of the catalyst. Encapsulated gels were kept in dry acetone for18 hours at 20° C. The gel systems used for this test are given in Table9.

                  TABLE 9                                                         ______________________________________                                        Gel Systems Used in Testing of Solvent-Triggered Release of the Catalyst                             Weight of  Volume of                                   ID                     encapsulated                                                                             dry acetone                                 No.  Sample            gel, mg    added, ml                                   ______________________________________                                        1    DMAAm gel crosslinked by                                                                        281        2                                                DEGBAC                                                                   2    DMAAm gel crosslinked by bis                                                                    135        2                                           3    NIPA gel crosslinked by bis                                                                     521        4                                           ______________________________________                                    

Following swelling of the gels in acetone for 18 hours, 1 ml of thesolution surrounding the gels was withdrawn and placed into anoligomeric product composed of the ester formed from adipic acid and 1,4cyclohexane dimethanol. An isocyanate was then added as shown in Table10. The resulting mixtures were quickly stirred and immediately placedinto an oven at 60° C. where hardening of the liquid surrounding theencapsulated gels was monitored. The results of the release test areshown in Table 10. "+" represents complete hardening which manifestspolymerization of isocyanate/polyol/acetone mixture within 5.0 min at60° C. "-" represents the absence of the viscosity increase in thepolyol/isocyanate/acetone mixture under identical conditions.

                  TABLE 10                                                        ______________________________________                                        Results of Testing of Solvent-Triggered Release of the Catalyst from          Encapsulated Gels                                                                              Weight of                                                                              Weight of                                           Acetone component                                                                              polyol, g                                                                              isocyanate, g                                                                           Result                                    ______________________________________                                        ID No. 1 (Table 4), 1 ml                                                                       1.3      2.4       +                                         ID No. 2 (Table 4), 1 ml                                                                       2.1      1.9       +                                         ID No. 3 (Table 4), 1 ml                                                                       2.2      2.4       +                                         Dry acetone, 1 ml, 20 mg catalyst                                                              1.9      1.7       +                                         added (Control 1)                                                             Dry acetone, 1 ml, (Control 2)                                                                 1.9      2.5       -                                         ______________________________________                                    

6.4 Shear-Triggered Catalyst Release from Encapsulated Gel

Encapsulated gels particles were sheared into smaller particles andimmediately placed into an oligomeric product composed of the esterformed from adipic acid and 1,4 cyclohexane dimethanol. Isocyanate wasthen added. The resulting mixtures were quickly stirred and immediatelyplaced into an oven at 60° C. where hardening of the liquid surroundingthe encapsulated gels was monitored. The results of the release test areillustrated in Table 11. "+" represents complete hardening whichmanifests polymerization of isocyanate/polyol mixture within 5.0 min at60° C. "-" represents the absence of the viscosity increase in thepolyol/isocyanate mixture under identical conditions (1:1 w/w) mixtureat 60° C.

                  TABLE 11                                                        ______________________________________                                        Shear-Triggered Release of Catalyst From Encapsulated Gels                                Weight of                                                                     encapsulated                                                                            Weight of                                                                              Weight of                                      Sample      gel, mg   polyol, g                                                                              isocyanate g                                                                          Result                                 ______________________________________                                        DMAAm/DEGBAC                                                                              180       3.5      2.2     +                                      gel mechanically                                                              sectioned                                                                     DMAAm/bis gel                                                                             250       4.3      2.6     +                                      mechanically sectioned                                                        NIPA/bis gel                                                                              220       2.7      1.8     +                                      mechanically sectioned                                                        Intact DMAAm/                                                                             330       1.9      2.2     -                                      DEGBAC gel                                                                    (Control)                                                                     ______________________________________                                    

GELS CAPABLE OF SWELLING IN HIGHLY REACTIVE ORGANIC COMPOUNDS Example 7

A mixture of 10 mL (97 mmol) dimethylacrylamide (DMAAm, monomer) and aspecified amount of ethylene glycol dimethacrylate (EGDMA, crosslinker)was deaerated by N₂ bubbling for 0.5 hours. Then; 100 μl of freshlyprepared 80 mg/ml solution of 2,2',-azobis (2-methylpropionitrile)(initiator) in DMAAm was added. The solution was stirred and placed intoa bath at 70° C. Polymerization with liberating heat was observed within1-2 hours. Polymer gel samples were slowly cooled down to roomtemperature and kept in sealed vials. Data on swelling of polymer gelsamples having various degrees of crosslinking are illustrated in Tables12 and 13. Swelling experiments were run for 2 days at room temperature.

                  TABLE 12                                                        ______________________________________                                        Swelling of Poly(dimethylacrylamide) in 1,6-Diisocyanatohexane (HMDI).        Polymer EGDMA/DMAAm  Weight dry,                                                                             Weight  Uptake,                                fraction No.                                                                          molar ratio  mg        swollen, mg                                                                           %                                      ______________________________________                                        1       No crosslinker                                                                             93        dissolution                                    2       1:2000       101       790     680                                    3       1:1000       150       1290    760                                    4       1:667        69        560     710                                    5       1:500        46        360     680                                    ______________________________________                                    

                  TABLE 13                                                        ______________________________________                                        Swelling of Poly(dimethylacrylamide) in Poly(propylene glycol)-               bis(2-aminopropyl ether) (PPGBAE, JEFFAMINE ® D-230).                     Polymer Gel                                                                           EGDMA/DMAAm  Weight dry,                                                                             Weight  Uptake,                                fraction No.                                                                          molar ratio  mg        swollen, mg                                                                           %                                      ______________________________________                                        1       No crosslinker                                                                             38        dissolution                                    2       1:2000       130       290     120                                    3       1:1000       85        230     170                                    4       1:667        81        190     140                                    5       1:500        99        290     190                                    ______________________________________                                    

Example 8

A mixture of 10 mL (97 mmol) dimethylacrylamide (DMAAm, monomer) and 30μL (146 μmol) ethylene glycol dimethacrylate (EGDMA,crosslinker) wasdeaerated by N₂ bubbling for 0.5 hours. Then, 50 μL of freshly prepared300 mg/ml solution of ammonium persulfate (initiator) and 10 v/v %N,N,N',N',-tetramethylethylenediamine (promoter) in drieddimethylsulfoxide were added. The solution was stirred and placed into arefrigerator at 3° C. Polymerization was observed overnight. Data onswelling of the resulting polymer gels are shown in Table 14. Swellingexperiments were conducted for 2 days at room temperature.

                  TABLE 14                                                        ______________________________________                                        Swelling of Poly(dimethylacrylamide) in Poly(propylene                        glycol)bis(2-aminopropyl ether) (PPGBAE), 1,6-Diisocyanato-                   hexane (HMDI), and Dibutyltin dilaurate (DBTDL).                              Swelling agent                                                                          Weight dry, mg                                                                           Weight swollen, mg                                                                           Uptake, %                                 ______________________________________                                        HMDI      107        730            580                                       PPGBAE    180        460            160                                       DBTDL     120        140             17                                       ______________________________________                                    

Example 9

A mixture of 5 mL (35 mmol) diethylacrylamide (DEAAm, monomer) and 15 μL(73 μmol) ethylene glycol dimethacrylate (EGDMA,crosslinker) wasdeaerated by N₂ bubbling for 0.5 hours. Then, 30 μl of freshly prepared300 mg/ml solution of ammonium persulfate (initiator) and 10 v/v %N,N,N',N',-tetramethylethylenediamine (promoter) in drieddimethylsulfoxide were added. The solution was stirred and placed into arefrigerator at 3° C. Polymerization was observed overnight. Data onswelling of the resulting polymer gel samples are illustrated in Table15. Swelling experiments were conducted for 2 days at room temperature.

                  TABLE 15                                                        ______________________________________                                        Swelling of Poly(dimethylacrylamide) in Poly(propylene                        glycol)bis(2-aminopropyl ether) (PPGBAE), 1,6-Diisocyanato-                   hexane (HMDI), and Dibutyltin dilaurate (DBTDL).                              Swelling agent                                                                          Weight dry, mg                                                                           Weight swollen, mg                                                                           Uptake, %                                 ______________________________________                                        HMDI      99         880            790                                       PPGBAE    46         280            510                                       DBTDL     100        240            140                                       ______________________________________                                    

Example 10

Dimethylacrylamide (DMAAm: monomer) of a volume of 10 mL (97 mmol) wasdeaerated by N₂ bubbling for 0.5 hour. Then, 0.3 mL of ethylene glycoldimethacrylate (EGDMA,crosslinker) saturated by benzoyl peroxide wasadded. The mixture was stirred quickly and following addition of 15 μLof N,N,N'N'-tetramethylethylenediamine (promoter) was added, and thesolution was kept a 3° C. Gelation was observed within 10-15 minutes.Polymerization was allowed to continue overnight at room temperature.

A transparent, homogeneous gel was formed and easily crashed into smallpieces by stirring. Microscopic investigation showed the presence ofsmall particles of irregular shape (i.e. effective size 20 microns andsmaller). The data on the swelling of the gels are reported in Table 16.

                  TABLE 16                                                        ______________________________________                                        Swelling of Poly DMAAm/EGDMA Gel for 2 days in Adipoyl                        Chloride (ACI) and 1,6-Diisocyanatohexane (HMDI), at 20° C.            Swelling agent                                                                          Weight dry, mg                                                                           Weight swollen, mg                                                                           Uptake, %                                 ______________________________________                                        ACI       32          83            160                                       HMDI      42         160            280                                       ______________________________________                                    

Example 11

A mixture of 5.0 ml (46.1 mmol) ethyl acrylate (EtAc, monomer) and 50 μlof 0.0226 ml/ml solution of ethylene glycol dimethacrylate (EGDMA, 5.99μmol; crosslinker) in dimethylsulfoxide was deaerated by N₂ bubbling for0.5 hours. Then, 100 μl of freshly prepared solution of 100 mg/mlbenzoyl peroxide in ethyl acrylate was added. The solution was stirredand allowed to stay at 70° C. overnight until formation of a softpolymeric gel network was completed. Data on swelling of the gel in PI,HDMI and PPGBAE are illustrated in Table 17.

                  TABLE 17                                                        ______________________________________                                        Swelling of PolyEtAc/EGDMA Gel for 2 days in Phenyl                           Isocyanate (PI), 1,6-Diisocyanatohexane (HMDI), Poly(propylene                glycol)bis(2-aminopropyl ether) (PPGBAE) at 20° C.                     Swelling agent                                                                          Weight dry, mg                                                                           Weight swollen, mg                                                                           Uptake, %                                 ______________________________________                                        PI        140        2700           1830                                      HMDI       74        1010           1260                                      PPGBAE    134        1240            825                                      ______________________________________                                    

Example 12

Two polymers were tested for swelling behavior in isocyanate. The firstwas polystyrene which was obtained commercially from Aldrich.Polystyrene did not swell in isocyanate. The second polymer wasstyrene-vinyl pyridine copolymer gel. The gel was prepared as follows:1.07 ml 4-vinyl pyridine, 440 μl styrene, 86 μl divinyl benzene and 4 mgAIBN were mixed in 10ml DMF. The solution was degassed by runningthrough nitrogen for about 10 minutes. The pre-gel solution was put at70° C. for overnight to obtain strong clear gel with light yellow color.A piece of this copolymer gel was put in toluene, the gel collapsed andbecame completely opaque. Then the gel piece was put in isocyanate, andthe gel swelled and became clear. This process was reversed within shortperiod of time, i.e., a clear swollen gel in isocyanate was collapsed intoluene and became opaque, the same piece of gel was put back inisocyanate and it swelled and became clear again. After one day, the gelswollen in isocyanate hardened (and still remained clear). Presumably,the pyridine groups catalyzed a polymerization reaction of isocyanate.

ENCAPSULATION OF REACTIVE CHEMICALS INTO LYOGELS

In Examples 13-15, encapsulated lyogels are swollen with nonaqueousreactive chemicals which are capable of holding the reactive chemicalsintact upon prolonged contact with aqueous solutions. This is presumedto be due to the hydrophobic properties of the encapsulating layer.

Example 13

13.1 Gel Synthesis

A mixture of 3.05 g (24 mmol) diethylacrylamide (DEAAm, monomer) and 55μL (0.29 mmol) ethylene glycol dimethacrylate (EGDMA, crosslinker) wasde, aerated by N₂ bubbling for 0.5 hours. Then, 20 μL of freshlyprepared saturated solution of ammonium persulfate (initiator) in drieddimethylsulfoxide and 10 μL N,N,N',N',-tetramethylethylenediamine(promoter) were added. The solution was stirred and allowed to stay atroom temperature overnight producing a transparent polymeric network.Then, the solution was heated to 70° C. where polymerization wascompleted within 2 hours.

13.2 Isocyanate Loading

A cube-shaped piece of polyDEAAm gel (dry weight 258 mg) was contactedwith an excess mixture of 0.2 g of trimeric hexamethylene diisocyanatein the isocyanurate form per 1 ml of THF. The gel was allowed to swellin the mixture for about 3 hours at room temperature under constantagitation. The weight of the swollen gel was measured to be 707 mg,resulting in a total uptake of 174%. The swollen gel was vacuum driedfor 3 hours. The weight of the dried gel was measured to be 348 mg,resulting in an isocyanate loading of 35%.

13.3 Gel Encapsulation

Poly DEAA_(m) gel swollen with isocyanate was sectioned into pieces inorder to ensure identical properties of the resulting Fraction 1 andFraction 2. Each fraction was placed into a separate vial containing anexcess of an oligomeric product composed of the ester formed from adipicacid and 1,4 cyclohexane dimethanol and dibutyltin dilaurate (1 wt % inpolyol) for about 14 hours at room temperature. The liquid surroundingthe gels hardened, indicating encapsulation of both fractions. Afterencapsulation, a transparent viscous polymeric film was visuallyobservable around each gel.

Each fraction was removed from the polyol/catalyst mixture and placedinto a separate vial. Fraction 1 remained intact and Fraction 2 wasfurther sectioned into smaller pieces. The transparent encapsulatinglayer around Fraction 2 pieces was completely destroyed.

13.4 Demonstration of Successful Encapsulation in Water

An excess of deionized water (pH 5.3) was put into a series of vials:one vial contained encapsulated Poly DEAA_(m) (Fraction 1) and anothercontained non-encapsulated poly DEAA_(m) gel (Fraction 2). A whitepolyurea layer formation was observed within 15-20 minutes around theFraction 1 particle, leaving the bulk of the encapsulated gel particletransparent. Small pieces of the non-encapsulated sectioned gel(Fraction 2) became completely white and no transparent areas wereobserved. The results indicate that the encapsulation shell prevents asubstantial part of the isocyanate loaded into the gel from reactingwith water. This may be attributed to the hydrophobicity of the polyolcomponent of the polyurethane layer formed around the gel duringencapsulation.

Both Fractions were allowed to stay in water for 1 hour at roomtemperature without agitation. The gels were then carefully removed fromthe water, surface cleaned free of liquid, and dried under vacuum for 1hour.

13.5 Test of Isocyanate Release from Gel

The dried gels were weighed out and placed into dry THE in such a waythat either Fraction 1 (the encapsulated gel) or Fraction 2 (thenon-encapsulated gel) constituted a suspension of 40 mg of gel per 1 mlof THF. This was done to compare the weight of released isocyanate perweight gel. Both fractions were allowed to stay in THF for 1 hour underconstant agitation.

Fraction 1 exhibited significant swelling and the white parts producedin 13.4 above were apparently dissolved in THF. Fraction 2 demonstratedsome swelling but the white polyurea layers were not removed.

THF solutions surrounding the gels were then analyzed by means of FTIRon a Perkin-Elmer Model 1620 spectrometer applying AgBr crystals. A peakat 2270 cm⁻¹ (--N═C═O vibrations) strongly suggests the presence ofunreacted isocyanate in the solution. As shown in FIG. 8, only thesolution that was in contact with the encapsulated gel contained anyisocyanate. No isocyanate was detected in the solution that hadcontacted the non-encapsulated gel. We conclude that a significantfraction of isocyanate was loaded into the gel and then onceencapsulated, was prevented from contacting the ambient water.

Example 14

14.1 Gel Synthesis and Swelling

A mixture of 5 mL (48 mmol) dimethylacrylamide (DMAAm, monomer) and 218μL (1.16 mmol) ethylene glycol dimethacrylate (EGDMA, crosslinker) wasdeaerated by N₂ bubbling for 0.5 hour. Then, 20 μl of freshly preparedsaturated solution of ammonium persulfate (initiator) in drieddimethylsulfoxide and 10 μl N,N,N',N'-tetramethylethylenediamine(promoter) were added. The solution was stirred and held at 3° C.Polymerization was observed overnight, resulting in a strong transparentnetwork.

PolyDMAAm gel (dry weight 630 mg) was allowed to swell in phenylisocyanate for 4 days in a sealed vial at room temperature. Theisocyanate uptake (i.e., weight of isocyanate per weight of dry polymer)was measured to be 1350%.

14.2 Gel Encapsulation

The gel produced in 14.1 was split into Fractions 1 and 2 andencapsulated as described in Example 13. Fraction 1 was left intact;Fraction 2 was sheared into small pieces as described in Example 13.

14.3 Demonstration of Successful Encapsulation in Water

Fractions 1 and 2 were placed in an excess of deionized water for 1 houras described above in Example 13.4. A slightly yellowish polyurea layerwas formed almost instantaneously around Fraction 1, leaving the bulk ofthe encapsulated gel transparent. Small sections of the non-encapsulatedgel (Fraction 2) became completely covered with the yellowish whitelayer and we observed no transparent areas. This indicates that theencapsulation shell formed in 14.2 prevents a substantial part of thephenyl isocyanate that was loaded into the gel from reacting with water.

The gels were then carefully removed from the water, surface cleaned toremove excess liquid, and dried under vacuum for 1 hour.

14.4 Test of Isocyanate Release from Gel

Dried gels produced in 14.3 were weighed out and placed into dry THF insuch a way that either (the encapsulated gel) Fraction 1 or (thenon-encapsulated gel) Fraction 2 constituted a suspension of 36 mg ofgel per 1 ml of THF. This was done to compare the weight of releasedisocyanate per weight gel. Both Fractions were allowed to stay in theTHF for 1 hour under constant agitation. Fraction 1 exhibitedsignificant swelling; the white parts produced in 14.3 were apparentlydissolved in THF. Fraction 2 demonstrated some swelling but the whitepolyurea layers were not removed.

THF solutions surrounding gels were analyzed by FTIR as described inExample 13. The spectra of the THF solutions (FIG. 9) suggest that thesolution in contact with the encapsulated gel contained much more phenylisocyanate than the solution in contact with the non-encapsulated gel.

Example 15

15.1 Gel Synthesis and Swelling

PolyDEAAm, synthesized as described in Example 13 (dry weight 590 mg),was allowed to swell in hexamethylene diisocyanate (Aldrich) for 4 daysin a sealed vial at room temperature The isocyanate uptake (i.e., weightof isocyanate per weight of dry polymer) was measured to be 960%.

15.2 Gel Encapsulation

The gel was split into Fractions 1 and 2 and encapsulated as describedin Examples 13 and 14. Fraction 1 was left intact and Fraction 2 wassectioned into small pieces as described in Examples 13 and 14.

15.3 Demonstration of Successful Encapsulation in Water

Fractions 1 and 2 were placed in an excess of deionized water for 1 houras described in Examples 13 and 14. A white polyurea layer formation wasformed almost instantaneously around the Fraction 1, leaving the bulk ofthe encapsulated gel transparent. Small sections of (thenon-encapsulated gel) Fraction 2 became completely covered with a whitelayer and no transparent areas were observed in these gels. Thissuggests that the encapsulation shell prevents a substantial part of thehexamethylene diisocyanate previously swelled into the gel from reactingwith water. The gels were then carefully taken out from water, excesssurface liquid wiped up, and dried under vacuum for 1 hour.

15.4 Test of Isocyanate Release from Gel

The dried gels were weighed out and placed into dry THF in such a waythat either Fraction 1 (encapsulated gel) or Fraction 2(non-encapsulated gel) constituted a suspension of 40 mg of gel per 1 mlof THF. We did this to compare the amount of released isocyanate perweight gel. Both Fractions were allowed to stay in THF for 1 hour underconstant agitation. Fraction 1 exhibited significant swelling and thewhite parts produced in 15.3 were apparently dissolved in THF. Fraction2 demonstrated some swelling but we did not observe any removal of thewhite polyurea layers.

THF solutions surrounding the gels were analyzed by means of FTIR asdescribed in Example 1. The spectra of the THF solutions contactedFractions 1 and 2 (FIG. 10) reveal that the solution contacting with theencapsulated gel contained much more hexamethylene diisocyanate than thesolution contacted with the non-encapsulated gel.

THERMORESPONSIVE LYOGELS

In Examples 16-21, thermoresponsive lyogels were produced. We observedthat the lyogels undergo transitions in neat organic solvents from acompact, opaque state at lower temperatures to an expanded, transparentstate at higher temperatures. The transition from collapsed, opaque gelsto the fully expanded, transparent gels in the solvent is reversible.

Example 16

16.1 Gel Synthesis

A mixture of 6.2 g (49 mmol) N,N-diethylacrylamide (DEAAm, monomer) and138 μl (0.58 mmol) di(ethylene glycol)bis(allyl carbonate) (DEGBAC,crosslinker) was deaerated by N₂ bubbling for 0.5 hour. Then; 20 μl offreshly prepared saturated solution of ammonium persulfate (initiator)in dried dimethylsulfoxide (DMSO) and 10 μlN,N,N',N'-tetramethylethylenediamine (promoter) were added. The solutionwas stirred and allowed to stand at 3° C. for 2 days. Completepolymerization was not observed, although an increase in viscosity wasobserved. At room temperature, we observed a hardening of the solutionand polymerization was completed at 70° C. in 2 hours, resulting in astrong transparent polymeric network.

16.2 Gel Performance

Sections (10-12 mg) of the gel were placed in excess dry DMSO where theywere allowed to swell overnight at 70° C., resulting in greatly expanded(8-12 fold weight gain) transparent gels. The DMSO in which gel had beenimmersed was cooled down to 40° C. and this resulted in formation ofopaque gels of diminished volume. The thermal transition from collapsed(opaque) gels to fully expanded (transparent) gels in DMSO was shown tobe reversible.

Example 17

17.1 Gel Synthesis

A mixture of 3.1 g (24 mmol) N,N-diethylacrylamide (DEAAm, monomer) and55 μl (0.29 mmol) ethylene glycol dimethacrylate (EGDMA, crosslinker)was deaerated by N₂ bubbling for 0.5 hour. Then, 20 μl of freshlyprepared saturated solution of ammonium persulfate (initiator) in drieddimethylsulfoxide and 10 μl N,N,N',N'-tetramethylethylenediamine(promoter) were added. The solution was stirred and placed into arefrigerator at 3° C. The solution polymerized overnight, resulting in astrong transparent polymeric network.

17.2 Gel Performance

Small pieces (10-12 mg) of the gel were placed in an excess dry DMSOwhere they were allowed to swell overnight at 70° C., resulting ingreatly expanded (8-12-fold weight gain) transparent gels. Cooling theDMSO in which gel had been immersed down to 35°-40° C. and also down toroom temperature, resulted in opaque gels of lesser volume. Thetransition from collapsed (opaque) gels to fully expanded (transparent)gels in DMSO was reversible.

Example 18

18.1 Gel Synthesis and Performance

N,N-Diethylacrylamide (0.89 g, 7 mmol) and ethylene glycoldimethacrylate (EDGMA, 17 μl, 0.084 mmol) were mixed with 9.0 mldimethylsulfoxide (DMSO) in a 20-ml vial which was then sealed with asleeve serum stopper. The solution was deaerated by N₂ -bubbling forapproximately 30 minutes followed by addition of 20 mg/ml2,2'-azobis(2-methylpropionitrile) in DMSO solution (100 μl). Thesolution was then kept at 70° C. over a two-day period. A transparentgel was formed and this gel collapsed and became opaque at about 40° C.When the gel was exposed to different temperatures from 20°-70° C., thegel underwent reversible phase transitions in volume and transparency.

Example 19

19.1 Gel Synthesis and Performance

N,N-Diethylacrylamide (0.89 g, 7 mmol) and di(ethylene glycol)bis(allylcarbonate) (DEGBAC, 21 μl, 0.084 mmol) were mixed with 9.0 mldimethylsulfoxide (DMSO) in a 20-ml vial which was then sealed with asleeve serum stopper. The solution was deaerated by N₂ -bubbling for 30minutes followed by addition of 20 mg/ml2,2'-azobis(2-methylpropionitrile) in DMSO solution (100 μl). Thesolution was then kept at 70° C. over a two-day period. This resulted information of a transparent gel which turned opaque at about 40° C.Temperature-dependent (20°-80° C.) phase transitions in volume andtransparency were reversible.

Example 20

20.1 Gel Synthesis

N,N-Diethylacrylamide (0.89 g, 7 mmol) and N,N'-methylenebis(acrylamide)(bis, 13 mg, 0.084 mmol) were mixed with 9.0 ml dimethylsulfoxide DMSOin a 20-ml vial which was then sealed with a sleeve serum stopper. Aseries of micropipettes (0.1 mm internal diameter) had been insertedinto the vial prior addition of the liquid mixture. The solution wasdeaerated by N₂ -bubbling followed by addition of 20 mg/ml2,2'-azobis(2-methylpropionitrile) in DMSO solution (100 μl). Thesolution was then kept at 70° C. over a two-day period and this resultedin formation of a strong transparent gel which turned opaque at about40° C.

20.2 Gel Performance

A piece of the polyDEAAm/bis gel formed in 20.1 was recovered from themicropipette, placed into neat DMSO in a temperature controlled bath andthe external diameter of the gel was measured. The gel was maintained ateach temperature until an equilibrium diameter had been reached. Thetemperature-dependent behavior of the gel is illustrated in Table 18 andFIG. 11.

                  TABLE 18                                                        ______________________________________                                        Temperature-Dependent Behavior of poly(DEAAm) gel in Neat DMSO.               Temperature, °C.                                                                      Diameter, microns                                              ______________________________________                                        80             265                                                            70             250                                                            60             223                                                            55             198                                                            50             182                                                            45             167                                                            40             154                                                            35             138                                                            30             131                                                            20             120                                                            ______________________________________                                    

Example 21 ENCAPSULATION OF A REACTIVE CHEMICAL INTO LYOGELS FOLLOWED BYTEMPERATURE-TRIGGERED RELEASE

This experiment discloses a process of encapsulating reactive chemicalsinto thermoresponsive lyogels in which the reactive chemical can bereleased from lyogels at an elevated temperature in entirely nonaqueousfluids (ie., fluids which lack the presence of any water). The enclosedexample illustrates (1) gel synthesis, (2) gel loading with a reactivechemical, (3) release of reactive chemical, and (4) behavior of thereleased reactive chemical.

21.1 Gel Synthesis

N,N-Diethylacrylamide (0.89 g, 7 mmol) (DEAAm, Polysciences) andN,N'-methylenebis(acrylamide) (bis, 13 mg, 0.084 mmol) (Aldrich) weremixed with 9.0 ml neat dimethylsulfoxide (DMSO) (Aldrich) in a 20-mlvial which was then sealed with a sleeve serum stopper. A series ofmicropipettes (0.1 mm internal diameter) had been inserted into the vialprior to liquid addition. The solution was deaerated by N₂ -bubblingfollowed by addition of 20 mg/ml 2,2'-azobis(2-methylpropionitrile)(Kodak) in DMSO solution (100 μl). The solution was then kept at 70° C.over 48 hours, resulting in a transparent gel which turned opaque atapproximately 40° C.

21.2 Gel Loading with Reactive Chemical

A polyDEAAm gel, prepared as described above and equilibrated with neatDMSO at 20° C. for several days in its opaque state, was weighed (W₂₀=430 mg) and placed into a 20-ml vial containing excess of 0.5 mg/mlsolution of Phenol Red (A.C.S. reagent, Aldrich) in neat DMSO. PhenolRed is widely used as a reactive dye capable of responding to smallchanges in its electronic environment and was therefore chosen as arepresentative example of a reactive chemical. The vial was kept at 70°C. for 0.5 h during which time the volume phase transition was observedin the gel. It became transparent and swelled greatly (W₇₀ =540 mg).Simultaneously, coloration of the gel due to absorption of phenol redwas observed. The bright yellow gel was allowed to cool down to 20° C.for 3 hours. Then, the yellow gel in its collapsed, opaque state wasplaced in a fresh portion of 0.5 mg/ml solution of phenol red in DMSOand kept there for 0.5 h at 70° C. The process of gel loading wasrepeated 3 times, until the gel was bright yellow in its opaque state.

21.3 Gel Encapsulation

The polyDEAAm gel loaded with phenol red (W₂₀ =435 mg) as describedabove and equilibrated with 0.5 mg/ml solution of phenol red in DMSO at20° C. overnight was placed into trimeric hexamethylene diisocyanate(isocyanate) (Rhone-Poulenc HDTLV) for 10-15 sec and then quickly takenout and placed into poly(propylene glycol)bis(2-aminopropyl ether){formula CH₃ CH(NH₂)CH₂ OCH₂ CH(CH₃)!_(n) NH₂ } (diamine)(Aldrich) for10-15 sec where a whitish layer of polyurea formed immediately aroundthe gels. This method of placing the gel sequentially into isocyanateand then into diamine was repeated to thicken the polyurea layer. Theweight of the encapsulated gel at 20° C. was measured to be 1.03 g. Theencapsulated particle was placed into 5 ml of neat DMSO and kept therefor 0.5 h. No coloration of DMSO surrounding encapsulated gel wasobserved (see FIG. 12(a)). Then the vial with the encapsulated gel inDMSO was kept at 80° C. in a temperature-controlled bath for 1 h, whichresulted in swelling of encapsulated gel. (W₈₀ =1.11 g) Visible breakageof the polyurea encapsulating shell was seen, followed by the appearanceof the bright yellow color in DMSO, evidencing the temperature-triggeredrelease of the reactive chemical. Corresponding electronic spectrum inFIG. 12(b) reveals a very distinctive peak λ_(max) 407, A₄₀₇ 0.753)corresponding to bright yellow/orange color.

21.4 Behavior of the Released Reactive Chemical

The following experiments were undertaken in order to illustrate thereactivity of the phenol red released from the encapsulated gel uponelevated temperature. The DMSO solution into which phenol red wasreleased was collected and separated into 2 separate portions. Into thefirst portion, poly(propylene glycol)bis(2-aminopropyl ether) was addedresulting in 0.1 mg/ml solution. A color change in the solution fromyellow to blue was immediately observed (see FIG. 12(c) with the peaksat 579 and 407 nm). Into the second portion,2-acrylamido-2-methyl-1-propanesulfonic acid (Aldrich) was added,resulting in 0.5 mg/ml solution. Change of color from yellow to red wasalmost immediately observed followed by the appearance of the peaks at512 and 398 nm in the corresponding absorbance spectrum (see FIG.12(d)).

EQUIVALENTS

It should be appreciated by those skilled in the art that the specificembodiments disclosed above may readily be utilized as a basis formodifying or designing other methods and compositions for carrying outthe same purpose of the present invention. For example, it is within thescope of the invention for the first nonaqueous reactive material (i.e.the encapsulated nonaqueous reactive material) to be a polyol, apolyamine or the like. In this type of arrangement, the secondnonaqueous reactive material (i.e. non-encapsulated nonaqueous reactivematerial) may be an isocyanate, a multifunctional amine, anorganometallic, an acyl halide, an acrylate, an acid, an acid anhydride,or mixtures thereof. It should also be realized by those skilled in theart that such equivalent constructions do not depart from the spirit andscope of the invention as set forth in the appended claims.

What is claimed is:
 1. A composition of matter, comprising: athree-dimensional polymeric gel network wherein the gel networkcomprises a material selected from the group consisting of poly(N,N-disubstituted acrylamides), polyacrylate esters, polyalkylsubstituted vinyl ethers, polyglycol ethers and mixtures thereof, thepolymeric gel network having a first reactive material substantiallyfree of water incorporated within the interstices of the gel network,wherein the first reactive material is characterized in that, when thefirst reactive material is exposed to predetermined conditions, thefirst reactive material enters into a spontaneous chemical reaction orcatalyzes a spontaneous chemical reaction;a hydrophobic polymericencapsulation layer on an outer surface of the gel network; and anaqueous medium having the encapsulated gel network immersed therein,wherein the encapsulation layer provides a barrier to efflux of thefirst reactive material from the gel network and a barrier to influx ofthe aqueous medium into the gel network under predetermined conditions.2. The composition of claim 1, wherein the first reactive materialcomprises a material selected from the group consisting of anisocyanate, a multifunctional amine, an organometallic, an acyl halide,an acid, an acid anhydride, an acrylate, an epoxy and mixtures thereof.3. The composition of claim 2, wherein the first reactive materialfurther comprises a dye, a pigment, a colorant, an additive or mixturesthereof.
 4. The composition of claim 1, wherein the first reactivematerial contains a catalyst.
 5. The composition of claim 4, wherein thecatalyst is dibutyltin dilaurate.
 6. The composition of claim 1, whereinthe polymeric encapsulation layer is selected from the group consistingof a polyurethane, a polyurea and mixtures thereof.
 7. The compositionof claim 6, wherein the first reactive material contains an isocyanate.8. The composition of claim 7, wherein the gel network is a gel networkof polydiethylacrylamide.
 9. The composition of claim 8, wherein the gelnetwork is a gel network of polydimethylacrylamide.
 10. The compositionof claim 1, wherein the gel network is a responsive gel network.
 11. Acomposition of matter, comprising: a three-dimensional polymeric gelnetwork wherein the gel network comprises a material selected from thegroup consisting of poly (N,N-disubstituted acrylamides), polyacrylateesters, polyalkyl substituted vinyl ethers, polyglycol ethers andmixtures thereof, the gel network having a first reactive materialincorporated within the interstices of the gel network, wherein thefirst reactive material is characterized in that, when the firstreactive material is exposed to predetermined conditions, the firstreactive material enters into a spontaneous chemical reaction orcatalyzes a spontaneous chemical reaction;a hydrophobic polymericencapsulation layer on an outer surface of the gel network; and anaqueous medium having the encapsulated gel network immersed therein,wherein the encapsulation layer provides a barrier to efflux of thefirst reactive material from the gel network and a barrier to influx ofthe aqueous medium into the gel network under predetermined conditions.12. The composition of claim 11, wherein the encapsulation layercomprises a material selected from the group consisting ofpolyurethanes, polyureas and mixtures thereof.
 13. A composition ofmatter, comprising: a three-dimensional polymeric gel network whereinthe gel network comprises a material selected from the group consistingof poly (N,N-disubstituted acrylamides), polyacrylate esters, polyalkylsubstituted vinyl ethers, polyglycol ethers and mixtures thereof, thegel network having a first reactive material incorporated within theinterstices of the gel network, the first reactive material comprising amaterial selected from the group consisting of an isocyanate, amultifunctional amine, an organometallic, an acyl halide, an acid, anacid anhydride, an acrylate and an epoxy, wherein the first reactivematerial is characterized in that, when the first reactive material isexposed to predetermined conditions, the first reactive material entersinto a spontaneous chemical reaction or catalyzes a spontaneous chemicalreaction;a hydrophobic polymeric encapsulation layer on an outer surfaceof the gel network; and an aqueous medium having the encapsulated gelnetwork immersed therein, wherein the encapsulation layer provides abarrier to efflux of the first reactive material from the gel networkand a barrier to influx of the aqueous medium into the gel network underpredetermined conditions.
 14. The composition of claim 13, wherein thegel network is a responsive gel network.
 15. The composition of claim13, wherein the first reactive material contains a catalyst.
 16. Thecomposition of claim 15, wherein the catalyst is dibutyltin dilaurate.17. The composition of claim 13, wherein the first reactive materialfurther comprises a dye, a pigment, a colorant, an additive or mixturesthereof.
 18. The composition of claim 13, wherein the polymericencapsulation layer is selected from the group consisting of apolyurethane, a polyurea and mixtures thereof.
 19. The composition ofclaim 18, wherein the gel network is a gel network ofpolydiethylacrylamide.
 20. The composition of claim 18, wherein the gelnetwork is a gel network of polydimethylacrylamide.
 21. A composition ofmatter, comprising: a three-dimensional polydimethylacrylamide gelnetwork having an isocyanate incorporated within the interstices of thegel network, wherein the isocyanate is characterized in that, when theisocyanate is exposed to predetermined conditions, the isocyanate entersinto a spontaneous chemical reaction;a polyurethane encapsulation layeron an outer surface of the gel network; and an aqueous medium having theencapsulated gel network immersed therein, wherein the encapsulationlayer provides a barrier to efflux of the isocyanate from the gelnetwork and a barrier to influx of the aqueous medium into the gelnetwork under predetermined conditions.